I currently have a XFX 6870 and it's a great card.Can almost play any game on high settings.The 6850 is an entry level gaming card at 1080p.The 6870 is the next step up.
What are your full system specs?(CPU,RAM.etc.)
It all depends on how much your willing to spend.What game do you play and i'll look up some benchmarks?
Ok.I game at 1600x900 and I can almost max out every game.The 6870 is the way to go,imo.And it should easily fit into your budget.I plan on getting another 6870 for corssfire soon as I have the money.