I'm new to Crysis. New to PC gaming in general. I was playing Crysis and enabled the r_DisplayInfo in console to see my framerate. I was at the part of the game where you're dropped off with the other soldiers in the war zone (where artillery is blowing up all around you) and can understand a drop in my framerate at that point. I was playing with all settings on Very High/Custom (I have an autoexec.cfg) and was getting an average of 28fps while standing still, and drops to 15fps and below while running. I was also using the Rygel, rocks, palm trees, foliage, nanosuit, and grass texture mods. I removed the autoexec.cfg, all texture mods, and changed the graphics settings all to low. I was only averaging 30fps this time, with drops to about 25fps. I would consider this wildy ridiculous. What's going on here?

Also note: Vsync is disabled, 8X MSAA (or whatever AA it uses) on high but changed to off on low.

TL;DR: 15-28fps on Very High/Custom, 25-30fps on Low, WTF yo?!

-System specs-
OS: Windows 7 Home Premium 64-bit
GPU: Sapphire AMD Radeon HD 6870 1GB (not overclocked)
CPU: Intel i3-2120 @ 3.3GHz (dual-core)
RAM: 8GB Corsair Vengence
HDD: SATA 7200RPM