For that size of room and you're listening habbits, I think either a PB13-Ultra, PC-Ultra, PB12-Plus/2 would be perfect and have more than enough subwoofer to fill up that room even at loud volumes.
If you're on a budget though (and who isn't), a PC-Plus 20-39 or PB12-Plus would both be excellent choices and would certainly be enough for moderate to moderate-loud listening. They may get a little stressed when turned up to loud in that space though, but only minimally and still extremely unlikely it would ever bottom out.