gadgetnerd :
http://www.evga.com/forums/tm.asp?m=407279
and yes 2 SLI 280's will beat the quad 2900's gx2's
This is what I call the "Nvidiot" effect. It's marketing the high end that most people can't afford to sell the low end that doesn't perform better than the competition and lacks full support for Direct X.
Well, marketing works. Intel relied upon marketing during the Netburst days (but AMD's marketing can't get the Phenom out of it's rut). Nvidia has always relied upon marketing plus strong arm tactics like the Assassin's Creed patch ("The Way It's Meant to Be Payed"), and dodgy drivers like the Crysis demo water or the blurriness of the 7000 series.
Is the GTX280 in quad better than 2 3870x2's in CrossfireX? Probably (don't know what you mean by quad 2900 gx2's). Is it better than the 9800gx2 in SLI? Maybe. Overall, the results show that the GTX280 is a bad deal. It's not much better than Nvidia's recent last generation and it's horribly overpriced.
If you're in the category of someone who can afford 4 GTX 280's then go for it, but if you're not in that price range of lucky gamers, don't decide on ditching an 8800gts 512, a pair of 8800gt in SLI, a 9800gx2 or even a 3870x2 just for one or two of these. Just not worth it.
The GTX280 is as much of a refresh as the 4xxx series, leaving out Folding @ Home stuff. Used to hear Nvidia fans say that AVIVO or image quality didn't matter all that much, it's about game and Nvidia delivers the framerates. Now, we see an overpriced high end Nvidia card that relies upon something other than gaming to sell, because it loses to the last gen Nvidia dual GPU card and the last gen ATI dual GPU card is often in third place right behind the costly GTX280.
Get the GTX260 instead, if you like Nvidia, or the 4870 if you don't. We'll see if the later versions of the GTX280 bring yields that make a difference after a die shrink. I'll be interested in seeing how the 4870x2 performs, as that's in my price range later in the year.
If I hear that Nvidia tells people that drivers will improve GTX280 performance, or that the later die shrink of the GTX280 will change things, then I'll really LOL. It will be so much like what we've heard from ATI regarding improved Radeon performance or AMD regarding Phenom.