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!
Ken