I say get whatever is decent at a cheap price. I picked up the 768MB GTX 460 because I got it for $121 after all discounts. There was a deal about a week back for a $146 768MB version (evga) w Metro 2033.
I would wait till the next hot deal on the 768MB version. There will always be better cards and over the long haul, prices will just keep dropping
Where the heck do you find these deals, is what I want to know. $230 GTX 470, now $121 GTX 460-768? Where do you go for these??