Heh I went from 6850 crossfire to a 480 and play at your res. My main motivation was needing a little more VRAM, especially for 4X MSAA in BF3. Finding 480s for $200 plus the NV drivers also handling MSAA better in that game sealed the decision. Even though the 6850s are technically a bit more powerful with proper scaling. If those cards had more than 1GB I'd probably still be running them.
So without finding a great deal on used 6850s or something I'd say 480 too as it's still pretty much the best overall bang for buck right now esp given the 1.5GB frame buffer.
I may go 7850 2GB Crossfire next...
“i dont care what consoles have they dont have mouse and keyboard” -crazyeyesreaper