It really just depends on what games you play and if you mind running them at reduced settings.
My current rig is using a single 5870 for 3150x1680 Eyefinity. It's showing it's age for sure but it still has pushed every single game I've thrown at it including BF3 with mostly medium settings. If it weren't for the 1GB of VRAM I could probably do more.
My wife is still using a 4850. While she's not what I'd call a hardcore gamer it's still serving her needs for Sims3, WoW and the oddball game here and there.
Personally I'd wait for at least Kepler a few months from now. Even if they aren't huge jumps over Tahiti it should at least have an effect on the pricing. That's my suggestion anyways.