Freezing during gameplay, no BSOD.

I recently bought a new GPU (Sapphire Dual-X R9 280x oc edition) and when i tested the game for the first time i got a huge freezing when playing. At first i thought it was because of my old PSU (Cooler Master real power M520) so i decided to upgrade it to a new, stronger one, and i bought a Corsair CS750M but the freezing problem still persists. If i want to play without any freeze i have to downclock my GPU but honestly this is kinda pissing me off since i deliberately bought an OC edition and i can't play with it at its best. Any tips?

Then it means your gpu is faulty, no ifs buts or arguments.

return it for a replacement.

I forgot to say freezing appears only when i play FF, on other recently games it works fine without any downclock. I also tested it on various benchmark and no problems appeared.

That doesn't mean anything, unfortunately when simulating D3D9, a DX11 gpu can actually work harder than if it was rendering natively to Direct3D 11.