What core freq do you use? I have problems with stability with the card until I lower core to 1100 and undervolt it to 775, after that I've got memory to 2100 (with PBE timings, not Branko)
Usually I start testing using the following conditions:
CV: 800mV
PL: +25
CC: 1150MHz
MC: 1950MHz
"with PBE timings" - PBE timings usually work fine for me as well