What Sapiento said is true and i have had about exact the same fps with both ATI 5870, Nvidia GTX 660ti & AMD 7950 with the same i7 920 d0 that i always have oc to 3.8ghz since it boosts up Conan.
But like he said do reading before even trying to OC if your not used to it and make sure to read about your specific cpu & motherboard & memory