Impelled, I believe you are mistaken on this...
Generally a display advertising 120hz or 240hz is capable of displaying at the respective frame rate listed. It will do this with multiple frame flashes or will do this with motion interpolation to try to clean up an image and to reduce LCD motion blur. It (generally) only accepts NTSC/ATSC standard broadcast resolutions of 480i/60 to 1080p/24/60. But, some PC and non-standard resolutions are almost always accepted and should be detailed in the owner's manual.
For the original poster: Get a plasma.
Your room and situation sounds ideal for the best image quality you can get, and that comes from a plasma, not from an LCD. While you see plasmas advertised wtih 600hz subfield drive, it's truly marketing junk for plasma which has never needed frame interpolation to deliver the best image quality.
The VT series from Panasonic and the 8000 series from Samsung will give you a 64" or 65" image for a similar price to the 60" LCD models.
Samsung delivers about the best looking LCD image on the market, so they will look a bit better than the Sharp displays if you insist upon going with a LCD. But, given your room setup, I would strongly advise you against LCD, and would recommend a plasma for your setup if at all possible.