if you insist on SLI, get two 7900gs's.
i suggest you get either a single 7900gtx (for future SLI)
single 7900gtx would offer around the same performance, 256mb more memory (because two 256mb cards still means 256mb of video memory)
or, an x1900 or x1950 card if you are willing to give up SLI.
personally, i dont think crossfire is as good as SLI, but i do think that ATI cards are better than NVidia cards... not for performance per dollar either.
i mean i went and got a $465 card and it doesnt support FSAA and HDR at the same time, plus ati has avivo video converter...and theyre also developing physics drivers (Havok FX and boundless gaming) which will allow you to plug two cards into a system (say, an SLI board?) and use one card for accelerating the physics of a game. im not sure if the SLI boards will work, but i dont see why it wouldnt since aegia is just using a pci slot for their cards...
physics processors are pretty cool. they've even got a game you can buy for $60 to demonstrate the power of the cards, but games like UT2k7 will support physics cards and such, and i think even 3dmark06 supports it...
http://www.newegg.com/Product/Produ...on=aegia&Submit=ENE&N=0&Ntk=all&Go.x=0&Go.y=0
two 7900gt's (better than two 7900gs's) would give about 7000 or so in 3dmark06 and my 7900gtx gets a 6166 in 3dmark06... but the 7900gs has 4 less pipes and 1 less vertex shader in comparison with the 7900gt or gtx... and the clocks are lower. i highly suggest you get a 7900gtx or just an x1900 instead of dual cards. the performance per dollar will probably be a little better with a single card, and power consumption might be better too...
two 7600gt's wouldn't give near the performance that a 7900gtx would though. dont get two 7600gt's.
its ridiculous how much the cards cost isnt it? lol