I received a 7100 from Outlaw in error, which I used for a couple of weeks 'till my 770 arrived a week or two ago. I have:
Sony 400 CD changer
Outlaw 950
Outlaw 7100, and now the 770
Paradigm Studio 100 v.3
I've only used the system for 2 ch. stereo to date (bloody projector still hasn't arrived).
My room is 17 x 24 plus the foot of an L of ~ 16 x 16. Pretty much the same scale as your room. It's furnished with large black-out curtains on 3 sides and many rugs on a hardwood floor -- the sound is pretty 'dead'.

The 7100 sounds great, and it's quite loud enough -- probably can output more than your ears could stand. However, I noticed a big difference for what I would characterize as very dynamic music. Two example CD's I that demonstrate this to me are Prokovief's Alexander Nevsky and Metallica's Justice for All. Yep, I have a rather wide range of musical taste :-). I'm not sure how to describe the difference, but one notable things is that the music can be played even louder, but it still doesn't *sound* loud untill you try to talk with someone in the room. Another thing, perhaps related with the previous one, is that things sound clearer, more distinct.

Having said that, the difference isn't overwhelming, but I wanted the 200 W as there's less chance of blowing up the speakers (paradoxically having lower watts increases the chance of speaker damage). I have blown up speakers in the past :-( and my new Paradigms are way to expensive for that!

I hope my opinion helps you a bit!
Regards, Nicholas