the 280x is the amd equal to the 680 or the 770. It would be a waste of money going from a 670 to a 280x, 680, 770. The only "worth it" upgrade would have to be at a 780 or higher level. I would say overclock the 670 and wait for the prices to drop on the 780's/780ti and grab one of those or just wait for maxwell.