I wanna overclock my GPU sapphire HD 7870 Mhz Edition 2GB 256bit. Is that possible overclock an overclocked version?

possible, but careful with your temp and try not to touch the voltage on it

thanks mate ^^

U can, with some trials, the best safe temp is to stay around 6x degree celcius during full load.

but mine factory overclock is 75c on full load and 35c on idle.

Wow, that's kinda hot, I guess u can hit 8x C but just keep watching the temp...Use stock volt, overclock the core clock, then some memory clock...
Test for stability ... but gaming wont hit till 7X C I guess...whats the temp usually when u game like playing BF3?

when i start playing any games that required badd ass graphic. when it run on 99% load.. the max temp was 75c.. and idle was 32~35. i dont know why.

Yeah weird, as usual for stock, its temp seldom runs that high. U have GPU-Z? Right click to read the ASIC quality. What's your ASIC quality percentage?