try updating your motherboards bios first ( set first all bios settings to default) Which mobo do you have? Can you post bios screenshot here of the voltages and memory timinjgs it sets
it could just be that your CPU needs a bit more SA voltage to stabilize.
Now 4800C20 is pretty neat, it could be the CPU doesn't like it with the XMP settings or that your motherboard just sets incorrect ones...
We are still looking for a suitable feasible solution for all new 40 series cards
till now this is the current opinion by UL:
"I'd still suggest for now that we just start requiring ECC for competitive OC and not care that without it you would get higher FPS"