My most recent builds have focused heavily on future-resistance. Accordingly, the GTX6xx[Ti] cards are off the table, for their crippled Compute performance. It doesn't matter in today's games, but it might tomorrow. What if someone writes a great AI engine that can run on a GPU? Kepler would probably fall flat on its face. I'll give up a couple of FPS now to avoid that risk.
If either of these are outside of your budget, look for a HD7750 at the high end of your budget, or a GDDR5 version of the HD6670 a little lower. Be advised though, I just recently played some GW2 at 1600x900 on a HD6670, and I had to turn most settings to "low" to get playable FPS.