Hi, i have 2 options: i can get a Qx9650 + GTX 280 on a Intel chipset(x48) mobo or i can get a Q9450 + 2 GTXs 280 in SLI on a Nvidia chipset (680i, 750i, 780i?) mobo.
What games? Because a lot of games already run pretty well at 1920x1200 with an 8800gtx and ONE GTX280 is almost twice as fast or faster in a lot of games.
As a side note, I'm pretty sick of SLI and nvidia chipsets so I'm a little bias already. You probably don't need it anyways at 1920x1200. If you had a 30'' monitor I'd suggest looking at SLI...
I'd probably just get a x48 board, q9450 and an 280... Save the money, get some decent ram and other components... and wait for nahelem. That combo should give you a pretty powerful system for even a few years.
At 1920x1200, you're mostly GPU limited. So the Qx9650 won't provide a large enough performance increase over the Q9450 at that resolution to warrant the extra costs. On the other hand though, a single GTX 280 is already enough for most games at the resolution. And then there's the issue of Nvidia's chipsets being a little bit less stable, reliable, and cooler running than their Intel counterparts.
So my preference is the same as Zefram0911: neither and go with a X48 mobo, Q9450 and a single GTX280.