Off the top of my head, no, no links, but I can tell you the "realworld" differance between a 6600GT and a 6800.
They will both run low-res stuff fairly close in performance... however, the 6800 will start pulling away significantly if you either:
A) Run the system in a hi-res mode
B) Turn up the AA and AS filtering
In no case that I've seen will the 6600GT surpass the 6800... usually they are either neck and neck (at low res) or the 6800 will pull away from the 6600GT in the above listed cases.
Neither is a bad card, but if the price differance is only $30 bucks, the 6800 is a no-brainer (and the above examples is stock card comparison... the differance is even greater if you unlock the 6800 with RivaTuner).
Tiamat... I know ON THIS FORUM, there are probably a few folks with dual LCD's... but if you look at the overall number of computer users worldwide, and compare that with those that have LCDs over CRTs (a low percentage to begin with) and then further divide that by folks who have DUAL LCD's, it becomes a fairly silly low percentage that XFX caters to and makes all these great claims about dual DVI support to all 12 people in the world who actually have dual LCD setups. If you want to run dual LCDs, more power to you, but I would be SHOCKED if the percentage of dual-LCD users is anything over 1% of worldwide computer users.