So basically I've been having a lot of trouble with my computer crapping out on me, whenever I open a game actually, so I took it in to the shop. The guy said it wasn't the cards but rather windows, reinstalled it, and sent me on my way. 1 weeks later- craps out again every time, I reinstall windows, nothing. Now he wants me to pay $150 and upgrade to a 8800 GTS 6xxmb, and I'm wondering if it's worth it. It the difference in performance really that great, I mean I understand the benefit of single card setups but... Also, with the 9 series out would it really be much more money to upgrade to an even better card (i.e. is he trying to drop some last gen. stock on me?). Obviously I'd not like to go much above that price, maybe $50 at the most. Not sure how important this is but the games I play are usually Company of Heroes, CoD4, Oblivion, etc.
If you still want sli I would say a pair of 9600gt's would be a nice upgrade if you processor and ram are up to par. Dont get the 640m GTS, its too old. 8800GT or 8800GTS(g92 only) are great cards. toms graphics chart shows that in oblivion the 79gtx2 get 18fps, the old 8800gts get 23, a single 8800gt-oc gets 32. I recommend the new dual slot 8800gt from evga for a moderate upgrade from dual 7900gt's. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
test the 7900's in another system and then sell em on ebay. That might get you enough for another Gt if your system could keep up.
The 8800GTS 640MB is a considerable upgrade from your 7900GTs and at $150 it isn't a terrible price. 7 months ago they were $400. That being said, you can spend $150ish on an 8800GT right now from Newegg that is a better card than the 8800GTS 640MB. For a few more bucks you can get the 8800GTS 512MB which uses the 8800GT's newer G92 core that will run about 10% faster than the 8800GT.
Also, next month should be somewhat exciting as nVidia's GT200 cards will be releasing as well as ATI's 4xxx series cards. Supposedly these cards are going to be pretty boss. Perhaps purchase an eVGA card that way you can step up to a new card when its released if you get some extra cash and would like to go that route.
You can also pick up an 8800GTS 512meg (g92) for around $200, and as low as $169 after rebates in some places. Very, very strong card for ~$200.
Another good choice for slightly less is the 8800GT. It of course also is slightly lower performance than the GTS 512 version.
The 8800GTS 640 is not a bad card, but it is dated slightly. It is definetly worth $150 though and will also be an improvement over your 7900's.
150 for a 8800GTS 640 not 320 is worth it. There will be people who push the newer G92, but they are not even close in build quality to the G80 series. Discoduck shows a link to one of the few gt I would consider. 8800GT single slot coolers are steaming piles of sh&%. You didn't mention what your power supply was. "crapping out" is a bit vague. Is it rebooting, crashing to BSOD, or what? It could be a weakening power supply that is the culprit. How old is it and what are the specs of your computer? For what it's worth, I just "upgraded" to 2 9600GT SLI from a single 8800GTS 640 and the difference in games is negligible at best.
I've recently changed from the same graphics setup as yours. Moved onto 2x8800GT's now with 680i sli.
Sounds more like drivers or ventilation, or your processor not keeping up. Does your rig get very hot?
Need info like version of Windows/memory setup/games that cause the problem. (Crysis will make any outfit crash depending on settings).
Ya, he takes the cards and $150 and give me the 8800GTS. What happens is I try to start a game and it gets to the main menu or just past that (like in CoD4- as soon as I start a single player game it goes fine until the point where it transitions from the map video thing to the game, and then it's out.) It really just goes down in power, then when I start it back up I usually get that "windows encountered a problem" thing w/ a stop error. I can't recall what power supply it has right now, it's now with me, but the proc is an AMD X2 4800+. I have weird graphical problems too, sometimes stuff lke shadows with start flashing in and out like a strobe light, i'll get extreme streaks where it looks like someone grabbed something like the side of a building and pulled it across the screen to a point. Kinda hard to explain really.
edit: 1 gig of RAM (quality). It's all games. Oblivion won't get past the menu, CoD I already mentioned, Company of Heroes won't get past the skirmish menu. Those are the only ones I installed after I reinstalled windows.