Overclocking questions

ok so i recently overclocked my AMD PHENOM 11 X6 1090t to 3.8 via uping the multiplers and ran it through prime95 for 7 hours and it ran stable with no errors but when i went to go play battlefield 3 my gpu went higher than it ever has gone before but it was only the first gpu and it hit 70c and its never done that and i didnt touch gpu settings is it possible that me leaving the rest of the bios on default settings that it would up the pci voltage or something?????


Cpu: Phenom 11 X6 1090t 3.2Ghz -----> 3.8GHZ
Cooler: Thermaltake Frio
Ram: Kensington 16gb ddr3 1600
MB: Asus M4A89TD Pro/Usb3
GPU: Radeon HD 6990 4gb
PSU: Rosewill 1000Watt bronze edition

i mean i left the rest on auto

Might want to give this post a shot in the "Overclocking" section. I really don't have much OC knowledge and I'm going to be doing plenty of research and reading before doing it.