I have been having this problem since a few days:
I own a Gigabyte Radeon 6770 and a Sapphire Radeon 6770 Vapor-X (The Gigabyte card is the primary one) and I have not had any problems until now; when I am playing, the Gigabyte card shows a normal usage, but the Sapphire usage is 10% lower in Far Cry 2 and around 3% lower in Bioshock Infinite.
I have been testing another games and the results are almost the same.
I can not play Battlefield 4 now; the frames go down because of the "lazy" card.
It is not a temperature problem; both can get only 70º on FULL CHARGE, on normal circumstances they are around 60-65.
Has anyone had this problem? I even tried reinstalling Catalyst, installing both latest Beta and Non-Beta versions and the problem persists.
Thank for your help.