What kinds of games do you want to play? I would suggest finding benchmarks for those games, to see how various cards perform. A HD7750 might satisfy you now; you've specified "high," not "ultra" or "max" settings, but you might still not quite get the frame rates you want for newer and/or more demanding games. You'd be happy for a few months perhaps, then remorseful because it isn't quite getting the job done and you will have wasted your money.
What is your total budget? For $42 shipped you can get the VP-450 (the only non active PFC PSU I could recommend); for $132 shipped you can get this HD7770: http://www.newegg.com/Product/Product.aspx?Item=N82E16814127664
which also has a rebate on it (if you play that game and win); for $135 shipped here's a HD6850: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102908