Which one is faster in GPUGRID?

According to the performance chart at the bottom of the performance page:

 GeForce GTX 960    GTX 960    GTX 670
          2048MB     4095MB     2048MB
N       =  193         76        201
Average = 15.77h     16.43h     16.49h
Minimum =  8.1 h     11.1 h     10.1 h
Maximum = 24.3 h     24.4 h     30.3 h

So these two cards are almost identical regarding the processing time, however I would chose the GTX 960 because it consumes much less electricity.

I would choose the GTX 960 too. But there is a bit of a memory clock problem with the GTX 960/970/980 (but not the GTX 750 Ti). On all GPGPU work, the memory clock defaults to the lower "P2" state, apparently to protect the card from excessive heat, or maybe to avoid errors, as compared to the "PO" clock used for gaming.

The problem is describe here:
http://einstein.phys.uwm.edu/forum_thread.php?id=11044

The solution is to use Nvidia Inspector as described here:
http://einstein.phys.uwm.edu/forum_thread.php?id=11044&nowrap=true#136598

It works for me with only a slight increase in temperature, though I have not tried it on GPUGrid.