That's a quad core CPU, right? Download CoreTemp and monitor what happens to the CPU cores while you are playing. See if the fps drop coincides with any notable changes in CPU speed/temp in CoreTemp. For me, I had thermal throttling enabled in my BIOS settings, which automatically scaled down CPU speed when temps started to heat up. So I have major FPS drops every 30 seconds or so when the thermal throttling engaged. I would reckon you are having a CPU issue. If its not your CPU its your GPU. One or the other.