not sure about the room size, but i'm pretty sure it exceeds 4000 cu. ft.
I'm sure one would be sufficient, but with two, I'll get the flexibility of tuning low. oh, and I'm a bass freak. never had two of the same subs ... but two ultras puts me in shooting range of a second DD18. hmmm.
if you are going to use your setup more for HT and less of music, between the 100 and 40, I'd choose the studio 40. even with music, if you are not going 2.0 listening, the 40s plus sub would still be good enough.