I bought a 5870,so I wouldn't wait. By the time Nvidia's dx11 cards are out and available the weather will be nice and you won't be thinking of gaming. At least that's how I look at it.
I hear they are not shipping in till at least April.
2nd Tier Makers Unlikely To Ship Fermi Cards Until April - [H]ard|Forum
This is a good article also.
NVIDIA and its troubled GeForce 400 series