Overclock my card 850/1000 with stock voltage..
Everything went well 1 hour with 3dmark06 and
online/offline games for hours..But,whenever I play youtube or anything related
to flash player I got BSOD..Does that mean my OC isn't stable?
Take a close look at what your clocks are doing while watching that youtube video. I know for my 5850, it drops the clocks to 400/900. Stock is 765/1125, and my overclock is 950/1300. For some reason youtube (I havent checked other flash sources) really messes with the GPU clocks.
Personally, I have not seen any decreased stability.