Speaker Cable Questions

Opinions please:

(a) For lengths of approximately 25 feet, is 10 gauge wire preferred over 12 gauge? I suppose 10 gauge is always preferable to 12, or is it?  

(b) Everyone on this forum knows how expensive "quality" cables are. While I haven't checked extensively, I have yet to see any of these quality cables available in 25 foot lengths. if they were I would have to mortgage the house  to buy into them. So the question here is what are the "best" (somewhat subjective I know) cables at 25 foot lengths? (cost no object answers as well as costs commensurate with an Musical Fidelity M6si amp welcome).
C3d9caab 06f0 446c ae8e 46be61643ebagdhal
LAT International (and many other places I'm sure) will build you any length you want, and terminate the cable with the connector you want, and the quality will be excellent. Have you checked LAT? No affiliation.

There's no best. I remmeber when 22AWG "hookup wire" was the rage. Flat cables, ribbon cable, solid core, skin effect, keeping wire off the floor, short runs of coat hangar wire.
Thanks rail2rail. I just checked the LAT International website. " 900 SIGNATURE 2 WIRE speaker cable" is there best speaker cable and I could probably get away with a 20 feet run, so no need for for custom length. Interesting though that given their somewhat detailed description of their silverfuse process, they do not speak to the end result gauge of the wire. From the picture I glean it would be 12 gauge.
Try Signal Cable. They will make custom lengths for you, and are very good cables. Price won't break the bank, either. I've used them for many years, interconnects and speaker cables.
My system uses a 22 foot pair of Groneberg Quattro Reference speaker cable.  It replaced MIT AVT-1 and Audioquest Indigo Blue speaker cables.  It sounds great with no loss of power and they cost 1,200.00 for the pair terminated in spades.
I'm using Chord Odyssey 25ft I bought here. Thin gauge. Working dandy.
I'm using (2) 25 ft.stereo prs. of Kimber 8vs which are 9ga. with my Vandersteens with great success.Reasonably priced as well.I think both prs. ran in the $1100.00 neighborhood. Ckeck with Johnny R in Verona,NJ for current pricing.

I know I'll probably take just a little heat for this, but...  Home Depot 25' 12ga (yup, orange extension cords) should be sufficient and it's definitely a little more affordable than some of the other things mentioned above.  And we're not talking about the 12ga speaker wire that you can now buy there - buy a couple of 12/2 extension cords, fix the ends, and connect up. You can probably Google to find the former references to a past audio show in England where a certain speaker manufacturer was showing their wares using essentially that cable (and where we learned of this trick).  I've had those flat interwoven cables, proper fat speaker cable, etc. and we have to admit that the darned 12/2 is as good as all that ('specially if you're over 30 and by definition have non-teenager hearing).
Blue Jeans Cable. Top quality Belden wire, top quality connectors (including locking bananas which are great), very good strain relief, proper termination loading, excellent insulation, excellent shielding. Made in the U.S. by a very good company, and at reasonable prices. The online custom order system works extremely well for any sort of (long or short) custom length. 10GA, 12GA and some custom gauges available as well. 
I agree with mr_hosehead. Any decent 12AWG cable set will make a dandy speaker cable, if you're happy with the look and feel, and the quality of termination that you can muster. You have to have the right crimper tool and soldering iron tip/temperature, and skill to do 12AWG justice. 
I've also used Kimber 8VS in the length you require and was happy with the result. There is now a 12VS offered which I would consider, however. 
Thanks to everyone for their input. Mr_hosehead, not sure what you mean by 12/2. I do get your point about standard 12 gauge, and I further assume you mean the same when referencing orange extension cord. As for fixing the ends up, and to rail2rail's point, why use any kind of termination at all? Bare wire could arguably be "better" because there is one less item (piece of material, etc.) in the circuit. I use bare wire at both the amp and speakers now.
Sorry - 12/2 is just a reference to "12 gauge/2-conductor" extension cords, that classic HD orange cord.  There are also (and maybe more prevalent today) 12/3 cords that also have that separate ground wire and connection.  The 12/2 cord is usually just a little bit more affordable and all you need for speakers.  Also, you probably would do just fine with 14/2 at your 20-25' range and save a little more.  I've used soldered spade lugs and screw-type banana plus in the past and both worked well (the soldered lugs never came undone while a couple of banana screws will probably loosen over the years).
You can find AQ Type 8 around here and there as bulk…a great sounding cable bargain. Blacker blacks…middier mids…highs that won't kill your dog…a tone that says, "you're a wonderful person with great taste."
Mogami speaker cables are cheapish and very accurate.
Blue Jeans, as stated above, good quality, fair price.

I have used  Blue Jeans extensively before, they are not very good cables, actually, compared to Mogami, they are pretty bad.
I will 2nd both LAT & Signal Cable.
ZU Libtec are very good regardless of  price and for what ZU sells them on Ebay greatest value in audio.
AQ type 8 is a good value as well.

I've heard Blue Jeans quite a bit and if that was I could have I wouldn't listen to music much . YMMV 
Mogami 3103 and supra ply 3.4 are very problematic cables. The Mogami sounds very dark, heavy, slow and atmospheric with rolled-off highs. When i put it in my system it sounded like i thrown blankets to the speakers. I really felt sick with this cable on. The Supra Ply 3.4 has many problems ,too. The first big problem is the lead voacals which sound laid back and very muddy. You will not hear a thing of what the lead singer sings with this cable. The second serious probelm with this cable is its stereo image. It is not balanced and it draws the vocals to the left side. It's like the plane is leamning towrds the left side. That is very annoying.
I used yo have some signal cable on my system but they added a harsh sound then i made a test with a dealer friend who loves xlo cables, the difference was huge! But my budget didnt allowed me to change all my cabling to xlo so i started to search occ and cryo cables on the web hoping those properties presented on the xlo were the key. After a lot of research and reading i bougth some audio sensibility impact and some xlo, for the money the audio sensibility are great, no harsh, better and stable image, bigger soundstage, a little bit less gran xlo but lot better than signal cable. The only SC remains in my system is the silver digital cable.