+1 on MSI 660 Ti Power Edition Overclocked. Not sure what's up with tom's hardware or techpowerup, they have different results. I think 670 is way too expensive for the price, compared to the 660 Ti Overclocked edition . I know the Overclocking headroom for a factory overclocked card is lower, but it is guaranteed to run at that kind of speed. But if you want to try to overclock yourself, try getting this:
You are comparing a MSI factory OC of 660 Ti to a GTX 670 reference card with stock clock, this is going to shrink the performance margin significantly, MSI 660 PE/OC should be compared to MSI 670 PE/OC to make it more of a fair fight. I still expect the cheaper card to come in ahead in value/performance but it won't be as steep as factory OC vs reference card.
I am staying with 670 over 660 in my build because I rather have spend that $100 on performance of my video card over the following:
A Fancy Full Tower Case over Corsair 500R
32 G of Ram over 16G of Ram(16 is already overkill)
I7-3770K over I5-3470K as I don't need HT
A HDD( that could always be budgeted later and I have no need for now)
Blue Ray Burner+Sound card over DVD Burner+Mobo audio(the latter is already good enough for me)
Saving toward 660Ti SLI( I have enough budget next month for 670 SLI so no need).
If none of the above applies to you then go with the 660Ti and use the $100 you saved on something you deem worth a while over a increase in Graphic performance.