cmdrdredd
Lifer
I can do about 80fps in BF3 with the game maxed out if I turn off the frame rate cap. Probably the most demanding and relevant game out there right now. A third card or two next gen cards would take that up to 120 or close to it I would think.
Really demanding games are few and far between these days. In most games I get well over 120FPS. If gaming continues to not make ground breaking revolutionary jumps in visuals and correlating hardware demands - which seems likely with consoles not making much of a hardware leap in their up coming replacements - I think it's realistic.
Right now for the most part 2x 7970s or 2x 680s is overkill for 1080P with the goal of maxing out available games, but one of either is not quite enough. I think whenever we get the GTX780 & Radeon 8970 we are going to see a single card that smokes every game out there at 1080P. The hardware is really getting ahead of the software these days. Things like higher resolutions and higher refresh rates are about all that is pushing forward the need for the latest and greatest hardware sadly.
You do have the occational game like Metro 2033 that is really bad in the fps department. I don't see why from a visual standpoint though.