I put 2.1 SDK and 12.1 drivers and got those running 1200MH/s with 855/875/850 clocks and 1v on every card.
855 ~392
875 ~400+
850 ~388
But yes I'm going to sell all of them when ASIC's comes out.
Can you tell me how exactly you downgraded to 12.1/2.1? Did you do some tricks or something?