A few things... some products are no longer including xp drivers... you'd be far wiser going with vist64 then xp64.

Sli is for people with too much money to burn. If you want faster gra[phics card speed, but one of those uber expensive cards, but for 3d work and most gaming, you can get a graphics card under $300 that will do you just fine. Odds are the second sli card might give you an additional 10% framerate increase... not really worth the invested cash. Check Tom's hardware guise (google it) for the best video card bang for the buck broken down by pricing.

And other programs (like Vue6 Infinite) will love you for the extra ram.

Way too many people take way too many things way too seriously.