Korimaru

I can maintain a reasonable fps when there's no npcs on the map, but the moment I drop into any map with a reasonable about of npcs, I get around 15-25 fps, even if I set literally all of the settings to minimum. Here's my specs: Windows 7 64 bit AMD Phenom ii x4 955 Processor 3.20 ghz 12GB RAM Nvidia Geforce GTX 580 I know my cpu isn't the best, but I've seen videos on youtube of people recording on high settings at what looks to be about 45+ fps with the exact processor I have. Anyone know what could be holding me back?