A lot of it depends on your material and distance from screen. If you are going to be watching mostly DVDs from a good player and HD then I would go with the 92" wide screen unless you can't sit at least 11' back from that. If you are going to be using an XBOX with 480p games then you may want to make the image a little bit smaller on the screen for that, but that can be done through the aspect control button. IMO the XBOX stuff for 480p isn't quite as clear as DVDs. The 720p and 1080i stuff from the XBOX looks awesome, though.
Also, if you are going to be watching IMAX films that are in 4x3 then they will almost all show a little lower image quality than major Hollywood film DVDs. Then you will probably want to sit closer to 2x the image width back. Same kind of thing goes for watching regular TV - this projector won't really be the limiting factor for screen size to viewing distance for that.
--Darin