Originally Posted by iRev_olution
I believe you need to increase your power limit and voltage to sustain the higher clock speeds. You may see increased heat but as long as the temps don't hit 80+ you should be ok.
^ Yes a great point I failed to mention. I am assuming you are running your card with the Voltage / Power % sliders MAXed out in your fav overclocking app. If not, please do and try again. You want to try and keep your temps below 65C if you can. The card can HANDLE
up to ~90C safely, but you will be throttling all the way starting at ~65C. A custom fan curve is usually needed when overclocking beyond factory overclocks and especially when using a modified BIOS.