I seemed to fix this last night by editing the CFG and adding 2 lines.

seta r_multiGpu "0"
seta r_multithreaded_device "1"

I noticed that by default it sets this to multigpu 1 and multithread 0 - most everyone has more than one core so the multithread needs to be set to 1. and unless you're running SLI or cross fire multi gpu should be set to 0.

One odd thing to note is, after i set these in the config - and loaded the game i noticed it set them back to the old settings. After adding the lines to your CFG you can now change these settings from the console, so change them back to how it should be. Quit the game, restart and like magic no more stutter...

I know it's BS that we have to trouble shoot this our selves but this 100% fixed my lag, and i tried it with some random - and it solved his problem as well. Hope this helps if you have any questions feel free to email me at rastakin@gmail.com and ill try to help you out. peace.