Ask this question again in April and you will have a more definitive answer. Benchmarks for the new nvidia card will be released. Keep in mind that the new nvidia card is going to be $700 and it will be compared to the ATI $700 dual gpu 5970. The nice thing is that you are planning on waiting and the answer will most likley be obvious in a couple of months.
They will release budget versions in the future. Personally I like love the fact that they release the top end part first then follow up with the less expensive ones. This gives us early adopters a longer liefspan on the component and we don't have to wait any additional time for it to be released.
If you are playing in that price range for a video card then the questions will be:
1. Which card has the best benchmarks and in game framerates? (My money is on the 5970.... i doubt a single GPU card will be better, although it may be close, see info below.) Then that brings us to the 2nd question:
2. To PhysX or not to Physx.
This is the position i'm currently in. I had a card burn out on me back in October so i got an inexpensive nvidia 'interim' card. The 5000 series of ATI cards were announced but not readily available and nvidia hadn't delayed their release of Fermi at that point. I figured that i could use the interim card for physx if i went with Fermi or i could stick it in an HTPC if i went with the ATI 5000 series. I've been waiting to play batman AA until i could fully anable physx lol.
I've only used nvidia cards in my own computers, since the TNT days of yore. I've used ATI cards for some of the systems i've built at work and my wifes laptop etc. ATI's cards are good, nvidia cards have just been a bit better when i was purchasing.
As an FYI in regards to SLI / crossfire, it is best to buy the single fastest card that you can afford. For arguments sake, lets assume you have a $400 budget for your vid card. The $400 video card will outperform (2) $200 videocards. ie. the ati 5970 will outperform (2) 5830's.
In any case I found 'some' ***benchmarks***
The GTX480 beats the 5970:
29% in Call of Duty: Modern Warfare 2
61% in Borderlands
25% in Far Cry 2
28% in Resident Evil 5
18% in Media
***HOWEVER I do not believe those numbers at all and suspect that the test were tweaked or adjusted to favor the nvidia card. One main reason being is that the card isn't being released to the major hardware reviewers. The GF100 is just 11 days from release. If this card was the 5970 destroyer that nvidia claims then they would have this card at anandtech, hardocp, toms and similar for benchmarking. In Nvidias defense though most of the time their cards outperformed ATI's.
Here's an interesting article.
good luck bro!