I don't mean to sound too prudent...but I am a bit wary of overclocking a very expensive card which will go bust before warranty expires for whatever reason (not necesarily related to the overclocking)and the manufacturer will not honor thge warranty. That will be really bad luck.
Also...when U overclock...R U supoused to install better case cooling system than the one with which your case came with?
Also...when U overclock...R U supoused to install better case cooling system than the one with which your case came with?