DutchForce
Memory overclocking does not have much impact on folding.  I've tested it sometime ago and saw that ~5% higher Mem clock resulted in ~1% higher PPD.
 

Zuhl3156
Stanford frowns on us overclocking anything when Folding but we all do it anyway. What I've found is that no matter how far I OC my memory, MSI Afterburner only reads 3004 MHz while folding when it would read 4000 MHz while gaming. IDK if the Folding client limits it or not. Just my observations. I try to Fold at stock clocks to prevent data corruption which happens more often if video boards are overclocked. It happens whether OC or not it just happens less.

Maxwell GPUs will go to the P2 state (performance state) when you run compute software, like FaH, which does not reduce the Core speed but will reduce the Mem speed.  On my GTX970 (and also GTX980) it will lower the Mem speed to ~3000 MHz (~6000 effective) and GTX980 Ti to ~3300 MHz (~6600 effective).  You'll have to use Nvidia Inspector to increase the P2-state Mem speed, because you can not set the P2-state with Precision X or MSI Afterburner.