I forgot about the X850XT. I was really surprised to find that dual 6600GT, though. I didn't even know that such card existed. It is a good alternative to two 6600GT cards because it's like half the price. I wonder if you can do Quad-SLI with these?
You can't 'Quad' them because no external SLi bridge, so even SLi+SLi (
true Quad SLi doesn't exist yet) would be lane restricted on all cards. Compare the 3D1 layout to the GX2s and then think about how SLi works to see the reason for a major impedement. Also the areas in which such core power would be handy would be severely restricted by the shared 128MB. Far better to SLi 2 GF6800 with 256MB IMO, although in his case he's pointing to a 128MB GF6800.
Anywhoo, it would be slow-quad if at all possible, and currently would likely take an extra hack of the drivers to even enable it.
As a single card, neat (especially for testing), but not practical or even economical compared to alot of the current solutions out there (GF7600GT is bound to beat it in most if not all situations).