the problem is that some time ago i could easily make my card run at 640\1330 in benchmarks and at 625\1330 in all the games. it was absolutely stable! the voltage was 1.2-1.225. And all was just great. Then i found the way to overclock my mem to 730 and more. I was about to set up a new record for myself at 640\1520, but the core now isn't able to work properly.. temperature is ok.