well, I have to say that FOR ME the 7900 gtx sli makes a whole lot of difference compared to the 7800 gtx sli...
This evening I was home early dur to my father taking over part of my round, and I quickly plugged in the 7900's instead of the 7800's. and ran some Hardware OC benchies quickly just to see that on my screen's native resolution @ 1920*1200 all games now are playable at 4*aa and 16*af, this was totally different with the 7800's...
quake 4 UQ 1920*1200@ 4*aa, 16*af went from 27.9 to 48...
serious sam2 1920*1200 4*aa, 16*af
went from 35 average to 67 average!
cod went playable at 1920*1200 maxed out 4*aa, 16*af ( no more drops below 35...)
all these games were NOT playable at these settings be4...
so this means wih current gen games, playability with nice iq settings on big widescreen monitors DOES require 7900 gtx sli to work...

at 1280*1024 difference was MINOR between these different setups, only at 1920*1200 with eyecandy did the 7900 gtx's tear away...

they better "tear away" as they tear away any budget too:)

but in the end, they do!