Any 100 watt receiver should be more than you need.
I have to agree with Prpixel, I ran Matrix 802's (series I, which actually are like the 803s) and had an Aragon 4004 Mk II (200wpc) and if anything, I think they would have opened up more with some more power.
As far as a 100 watt receiver..... I really would think you'd do much better with amps, and with bigger amps given the speakers you are heading to. Yes, for now the CW's will sound OK with minimal power, as they are pretty efficient, but if you stay with low power...once you do upgrade the fronts (which I would highly recommend you do for synergy alone) you will be in the amp market again!
Learn from those of us who have gone through many (15+) systems to get where we (I) are (am), buy what you'll need, assuming you can afford it, or consider waiting until you can! It's usually cheaper than doing it all several times....sometimes not as much fun/frustration, but certainly cheaper!
As for your main question, I have a similar sized room, with 12-15' ceilings. I use 7 (seven) 200 wpc dual mono amps for my 5 speakers..... overkill? Maybe! But it sounds great, and doesn't give out at higher volumes...which I find HT's to really need! I think if you ran B&W's off even the best receiver, you'd find they'd still do better with good power amps. I personally find the B&Ws a little rough in the upper mids and highs, so I would recommend a smooth amp. McCormacks always seemed like a good match, but when I tried them (DNA 1) I found the bass less than satisfying after the Aragon.
Good luck and happy listening!
Having lived with the N805's for almost 5 years now I like to add some observations gleened from lots of experimentation and equipment changes.
1. Take the grills off when listening. This does wonders for the width of the soundstage.
2. The more power (current) the better.
3. Very revealing of downstream equipment.
4. Use good mass loaded (heavy) stands that are coupled to the floor.
5. Better to bi-wire.
6. Sit with your ear level with the tweeter.
7. Spend a little time tuning the room. Damp the first and second reflection points.
8. Give them some room to breath; about 3 feet into the room is good.
When you get them set up correctly they really sing. My N805sig's image sooo good that I like to trick people into thinking that they are listening to surround sound. Anyway, this tread was about amplifiers and I've gotten side tracked.
Amps that I've used with great success with my B&W's are Scientific audio research labs MOS400, Aragon palladium mono's and aragon 8008BB.
If your going to do the surround thing then I would say try one of the 5 channel amps from the following manufacturers: Macintosh, Aragon, Rotel, adcom or sherbourn. I've only had experience with the Mac amplifier but I will be trying the Sherbourn 7/2100 in my rig next week. I'm getting the urge to simplify. I'm currently using 6 amps for seven channels.
A used Parasound HCA 1206 gives you 135 watts/channel into six channels at 8 ohms (200 at 4), and you can bridge four of the channels into two channels for 350/ch. This is a good value at used prices of 700 to 900. I used one for years and finally sold it as I slimmed down my front room theatre system to speakers requiring much less power.
I'm running My surround(7.1) with 600w/ch(Bryston 14BSST) for front speakers, and 160w/ch(Bryston(BSST) l/r side, l/r rear,center. My speakers are B & W in wall equivalents of the 803s and HTM1 center with four CDm SNTs for surround. I agree that you are more likely to damage your speakers through clipping with too little rather than over driving them with too much power.