MSI 7870 Hawk is the best 7870 out there, and a stock 7870 with the new 12.11 drivers consistently beats the GTX 660 at 1080p and higher.
GTX 660 doesn't seem to scale too well with overclocking at the moment, due to the TDP limit and Power+ limit in AB Nvidia put on this particular card. Most reviewers have pushed the 7870 Hawk to 1300mhz on the core clock with relative ease, theoretically increasing it's lead over any non-ti gtx 660 if both were overclocked to the max.
It's too bad you didn't post this yesterday, the 7870 Hawk was on sale for $245 for the past couple of days on Amazon and Newegg, now it's back up to $260.
If you were to get a 7850 though, I would choose the PowerColor PCS+ 7850, most have been able to clock 1250mhz on the core since Powercolor cherry picks their PCS+ line. However, if you were to spend $215 on the PCS+ 7850, you might as well spend $230 on a 7870 as you'd still be under the $250 mark.
Edit: PCS+ 7850 is actually $195 on newegg right nowEdited by octiny - 11/7/12 at 11:55pm