Thanks! I have the exact same CPU and overclock as you and was having problems after the latest patch. I'll give this a try. Another temporary fix that worked for me was to simply alt-tab out and then back in again. The framerate issue comes back after about 5 or 10 minutes though.
Core i5 2500K @ 4.8 GHz || 16 GBs 1600 MHz DDR3 || Sapphire Radeon HD 7970 || Dual 128 GB SSDs