If the gtx 780ti and radeon hd 7990 were the same price which would you choose

780ti. Primarily due to the non-perfect scaling of the 7990, as well as the much higher power consumption.

I would only get the 7990 over the 780ti if crossfire scaling was more consistent, as well as more games were mantle capable, as mantle does improve crossfire scaling, even with top end processors.