I also read, in another post, that GRAW2 won't allow textures to be set to high unless you have over 512mb ram on the card, but wouldn't your dual 320mb cards show up as 640mb combined?
I need help here, i'll be ready to buy in about 10 days.
Unfortunately it doesnt work like that. Sli'ing 2 320 meg cards wont give you 640 megs...it will remain 320 megs. So, personally i would say the GTX would be a smarted buy for now and the future possibilities.