I am running 2 6800 GToc's from BFG and am very pleased with the outcome.
It is a couple of steps up, but my experiance with games such as BF Vietnam, 1942, Diablo II and CS Source have been worry free.
Have not read up on the X800's that everyone is speaking of though. Look for some reviews though and compair for what you play them on.
The heat sinks are also well suited for SLI.
Here is a Pic of my rig now that I have cleaned up the wiring.