I agree Frantz.
In fact I have been considering either 2 F113's and an F112 or 3 F112's or possibly even a pair of F212's as the new room won't be as big as my previous room
If you can be comfortable with them ending up with non-symmetrical positions in your room , I would still bet 3 F112' would give you better response than a single of anything (Including a single IFB --- IN MOST ROOMS). (or buy 4 F113's, solve the symmetry issue and put one near each corner to be measured for exact optimal position).
As to an IFB sub: When I built my room, I considered it but for the very same reasons I wouldn't use a single Thor, I preferred multiple subs.
As it turns out, for 25% of the cost of a single Thor, I get 4 well placed subs, incredibly clean headroom beyond my wildest imagination, almost 10,000 watts of power, 8 15 inch drivers and 4db's down at 5hz. My guess would be Steve can do close to the same thing for similar $ with some combination of JL subs.
Now, if I could have TWO (or more) IFB subs, that may be an entirely different story.