For those interested in the OS issue, I just booted off a Win 8.1 x64 drive, same rig, same settings, hash went from previous 720 kH/s (Win 10 x64) to 837 kH/s. Using ccminer-djm34-neoscrypt-65.
Now try Windows 10 Pro 64Bit. I believe you will go even faster. I did

In fact, as I posted earlier, my experience was quite the opposite. I was on Win 10 Pro x64 (as posted in the Mining Hardware Comparison chart) and going back to Win 8.1 increased my hashrate. Later on I might try to revert to Win 7, unless someone in this thread has already tested and found no difference between Win 8.1 (Pro x64) and Win 7 (Ultimate x64).