Quad ESLs - I have some questions

Recently I heard the latest model Quad ESL, 2905 I think, and it was a love at first listen kinda thing.  Of course I began looking at used Quad ESLs, and I am curious what the significant differences are between the 63s and the later models like 2805s and 2905s?  Used 63s are in my price range now, 2805s etc would require some patience, so I'm curious if the SQ, reliability, power handling, or other differences are worth the additional cost?  W/r/t 63s, should I be wary if they've been rebuilt. or should that be comforting if the rebuilder has a good reputation?  Anything else I should know?

The 2905s I heard were powered by a Bob Carver Crimson 275, the dealer said my BAT VK-55 would also be a great match.  I listen to singer/songwriter/acoustic/Americana/indy/alternative music with some experimental, jazz, chamber, and classical piano thrown in.  Think First Aid Kit, Jeff Parker, Wilco, Michael Kiwanuka, Gordon Lightfoot, Everything but the Girl, Anna Meredith, generally 85-93 dBs.  Room is 12x20x8, set up for one listener, fairly well treated.  Current speakers are Thiel CS-2.3s.  Also considering Zus and Devores.
Can't help you with the old versus new Quad comparison but totally get why you fell in love. I remember hearing a pair of 63s many years ago and being awestruck at the purity of the sound. The Quads aren't for everyone or every room so tread carefully. If you like that kind of midrange magic but want to be able to play your Americana/indy/alt music loud at times then consider a pair of Harbeth's or better still Daedalus (there are a pair of Athena's for sale here now). The Devores and the Zus are pretty good too but you will likely not feel the love for them the way you did for the Quads.

All well design ESL’s are great, the only area that they fall down is deep powerfull bass that moves the air in the room common theme of most esl/planer speakers. The only one that did move air was the old Maggie 3 panel Tympani with additional side wings making them 4 panels wide each, but they were the size of room dividers. http://usr.audioasylum.com/images/6/63369/image1.jpg (these don’t have the wings attached yet.)

It’s why my Monolith esl’s are xover at <150hz to great dynamic bass units, that can if needed, you feel through your body with organ notes, and hit’s hard in the chest with the dynamic snap of drums.

Crossing over any higher than 150hz is not advised, as it means the bass drivers are then getting into the lower mids, and you want to keep this for the esl, been there done that, no good

Cheers George
I have Quad 57s, rebuilt by Quads Unlimited. Great speakers. That said, I prefer my Bache Audio Tribeca speakers. Beautiful midrange with tight bass and overall a much better balanced speaker. 
i have the 63 and the 2.3. you might think about what else was different in the chain...they have different strengths for sure.
also you should check out the Emminent tech panels, probably sublime with your amp and room size and very affordable new
While I love quads and used to own 63’s with the full crosby mod, I got sick of getting panels replaced. Today you can buy refurbished panels, which cost much less, but still they have to be installed.

So do your homework and make sure you can deal with arced panels if needed (or have someone local that can do it for you) 

I feel like owning ’stats is an audiophile rite of passage.
Run , don't walk away from them . The panels have major issues . I was in the same situation about 3 years ago . I had read of some bad panels when I was researching the 2905 . I ended up buying a pair of the 2905's from a Hifi stores used section in MN . I had them for about a year and did somewhat enjoy them . I did not try enough gear with them to get the best sound out of them . I listed them on craigslist and quite a few months later I sold them to a guy . I have texted off and on with the buyer in the 3 years since selling the speakers . He told me a panel went bad and would cost around $1500 plus shipping to get them fixed . I have seen listings for the 2805 and 2905 recently as well with talk of the scratching noise you hear intermittingly once they start going bad . Not worth 4k for such short lifespan . If you bought a pair new maybe the dough to fix wouldn't seem so bad .  
I am going to try the Gr Research open baffle servo subs to go with my King Sound King stats . Everything ive read over the years makes me think it will be a flawless incorporation with stats . I am also considering one of his two open baffle speaker kits to buy and build as well . Heard they can compete with stats in the mids and treble but are better than the Kings bass .
To anyone considering an electrostat, trust me, if you can afford the space and cash, go for a Soundlab. There are only a few dealers, and I have not heard them in quite a few years, but they are so far superior to other ’stat design I have heard. And I’m sure the latest tech they have developed makes them even better.

If I ever had a dedicated listening room (and hope to someday), I would simply find the size and cost range Soundlab that suited me, and order without even auditioning them.

Having heard current and very expensive and respected other brands of ’stats, I’m shocked that people don’t hear the obvious shortcomings. A friend uses to own A1's and then U1's, so I have a decent amount of experience with them. 

As I stated I used to own Crosby Quad 63’s and currently own stat super tweeters that augment my TAD’s (which are very Quad like in sound), and yet I still dream of owning Soundlabs someday (but I'd keep the TAD)  It’s a shame that they’re not better known, displayed and marketed.  They are also a very good value and can be updated.

No brainer with the Sound Lab. Most everyone knows they kill Martin Logans etc. I was once convinced that dynamic drivers were the king of bass. Not so. Full range huge Sound lab electrostatic panels produce the cleanest, lowest distortion, detailed bass at high volume levels. Dipole bass. I am listening to my Martin logans right now. They stink. My old Acoustat 2 plus 2's sounded better. I might have to rob a bank for the Sound Lab's. They aren't cheap. Who cares about the size of them. Go big or go home. 
Sound Labs are the MOST coveted loudspeaker for any electrostatic fan. You have reached heaven when you can own a pair. Lower mass diaphragm plus its the engineering of the transformer that makes a huge difference. Martin logan uses 2 transformers both in the signal path in their loudspeakers. One to couple and the other to increase efficiency.  I am listening to my Logans now and they sound like sound coming from a metal trash can. Martin logan are just a STARTING point for an electrostatic speaker lover. 
Good advice, thanks all.  As usual, my list of options had broadened (Harbeth, Daedalus, Soundlab, Emminent, Bache) rather than narrowed. 
I guess I will stay away from the Quad ESLs for now.  I don't need a right of passage or another project right now or a fickle love interest, surely there are other paths to audio nirvana.  Thanks everyone for their comments and sharing your experiences!
thosb, keep an eye out on the used market. Both Acoustat and Sound Labs speakers are indestructible as long as nobody has gone into them.
You might trip across a pair at a good price. Once you have lived with one of these there is no going back. Everything else makes Kate Bush sound like Brad Roberts:)

They were magic ESL’s even by todays esl standard, BUT!! are all dying.
Stay away from the original Acoustat ESL’s 1, 1+1,2, 2+2, 3, 4, 6 and 8’s

All these now are having problems with the whole honeycomb plastic stators decaying with age, and becoming porous absorbing humidity, which allows for HT leakage arcing tracks to form like a cancer, mainly all around where they sandwich glued front and rear together. And once these cancerous tracks form that’s it good-by panel.

After all the plastic honey comb panels were originally just office fluro lighting diffuser covers, never meant to be insulated for 4kv esl voltage
These are Acoustat 4’s, notice the panels resemblance to office fluro diffusers?

And not to mention, the other problem they have, the 100’s of yards of stator wires becoming unglued from those honeycomb plastic stators, as the glue is now brittle and just lets go causing them to rattle.

Cheers George
Agree that Soundlabs are great having owned the Pristine model years ago.  The Quads as REBUILT by Electrostatic Solutions are amazing however.

I’m listening now to my Bache Tribeca’s and wondering if I would even bother to connect the Quads back up again. What’s special about it is the whizzer-less bamboo wide band driver. With nothing in between the driver and my amp it’s very smooth and coherent. 
If we're talking about 'stats you can't forget Sanders Sound Systems model 10e. A bit pricier than the Quads, but offer the best of both worlds. The most coherent sound from 170Hz to 20kHz+ and a very well integrated TL (transmission line) woofer system. Also, SSS includes an LMS (loudspeaker management system) that allows lots of adjustments (EQ, crossover, room correction and driver time alignment). And... they play plenty loud and are virtually indestructible with lifetime warranty. Sanders has the best customer support I've ever experienced.