Hiya Bray. I've got a 20-39 PCi in a 16x22 room w/ 10 ft. ceilings. It opens to a 14 x20 kitchen. I've got more than enough sub left over. The gain is at about 40%.

Having said that, I'd suggest you call the good folks at SVS. They are as terrific as the Axiom crew and will help you pick the right sub. Interestingly, they sold me a PCi rather than the Plus I had in mind and saved me some money. I like their approach of selling what's correct, not what the traffic will bear.