I used to have a BFG 8800 GTS OC2 with 320mb, but after some time it was defect, so i RMA'ed it. Since i could not wait 3-4 weeks for the RMA to return i went out to buy a Sparkle 8800gts but with 640mb.
Now i have both cards (Just got a brand new BFG back from RMA).
Normally i would just use the 640mb one offcourse, but since the BFG is an OC2 version wich is oc'ed i wassnt sure anymore.
I have a 22" widescrren and im getting a 24" soon, so i game at 1680*1050 atm and probably 1900*1200 or whatever the new 24" screen supports.
So sell the 320mb version - grab another Sparkle 640mb and a new mobo and put in sli? or just sell the 320mb and save the money for now?
Sell the 320mb, but don't worry about changing your mobo (would be a real pain in the ass). See how the 640mb works with your new monitor, and if you need more juice wait about a month and a half until the GPU makers release their refresh cards. At that point you will probably be able to get a single card solution that will game at 1900x1200.
Assuming its the same Sparkle, they make pretty decent PSUs. I have no idea if their GPUs are on par but then as long as they use a reference design I don't see a way they could really mess it up. Although I'm not too knowledgeable about all the non-mainstream brands, I haven't heard of any that you really need to stay away from with newer gen cards.
At the higher rez the 640MB should help more than the OC but its not a trend I see on Tom's VGA charts. I'd bet with newer games like Bioshock, Lost Planet, and Crysis will show this trend though.
The Sparkle Calibre 8800 GTX: just like any other 8800 GTX, but it has a TEC cooler that keeps the card 10 degrees cooler than other 8800 GTX cards. So far so good, right? Now here's the problem: it consumes more power, it costs more, it makes more noise, and the total heat generated inside the case is actually more than with other cards. It was a very nice try, but it didn't work IMO.
@OP: sell the OC2, especially if it's still sealed so you can prove it's brand new and unused. 6 months from now sell the Sparkle too, and get yourself the latest and greatest high-end card out there. I assume you have the money - few of us here would spend $400 on a new card just to avoid waiting 3 weeks for the replacement card. It will be a better choice than GTS SLI.