Here are pics of the cards that I have had over the last few months.
http://i867.photobucket.com/albums/ab234/davanius/asus670back_zps4b424e94.jpg
http://i867.photobucket.com/albums/ab234/davanius/gigabyteevga_zps03a197e0.jpg
http://i867.photobucket.com/albums/ab234/davanius/20120328_130455.jpg
I had the 7950 top earlier last year.
The 7950 and gtx 670 Windforce editions had the coolest temps matching the 7950 top but that is a 3 slot cooler. All under 70c on auto fan profile.
The EVGA FTW SIG 2 had the highest stable overclock at 1254 mhz with temps reaching 75c average and the ASUS dcu2 670 getting a stable 1241 which is good considering it's not the top edition. Temps were 72c average.
Both cards were on auto fan profile.
The ASUS dcu2 has a base clock of only 915 but boosted out of the box to 1124.
The 7950 is the best value card imo but I found that the 670's gave smoother and more consistent frame rates across a wide variety of games.
My Windforce 670 didn't overclock very well at all. Out of the box it has a 980 base clock and boosted to 1137 mhz. Stable overclock only reached 1154 mhz, so I got a poor overclocker.
The ASUS cards are the quietest imo. I could not hear the card until I increased the fan speed to 80 percent.
The Windforce cards were the coolest.
And the EVGA was the fastest.
Build quality goes to ASUS then EVGA imo.
Be aware that the ASUS dcu2 gtx 670 has 2 green led's next to the power inputs. They are quite bright and they don't turn off when you power down.
Good post; useful bit of info there.

Out of interest, what would you say with regard to the differences in image quality (if any)?