Guys, the vast majority of lag in m2tw is from your cpu, dealing with the individual units.

Since sprites are used past a certain distance, graphics have very little effect (once you get to a decent level of card).

The 7800gt 256mb has no problems (i'm using one ;) ) and if you look up the benchmark results, you'll see what i mean about the 6600gt 512 (and why you'd run two in sli when you could easily get a decent card is beyond me)

/rant