I'm pretty sure it's your GPU. This game is actually fairly GPU-intensive even at low settings; my R9 380 is utilized 15-25% on 640x480, all low, with 160FPS (capped). I have a similar CPU (equivalent to a Q9550 @ 4GHz) and I have no drops in that spot. The game also uses around 600MB VRAM at those same settings. Would be nice if that was optimized. I wonder how hard it would be.
My style is generally pretty flexible, by which I mean, I randomly go super aggressive and get raped by spam nades or super defensive and get choked out of all items. Also probably the player who knows the least amount of trick jumps (still can't do stairs to mega on Catalyst reliably).