Forgot to add steps to reproduce.
1.Crouch
2.Hold W+A
3.Press turbo for a second or two
4.Will now be running standing up

100% usage in the menus on my gpu then 60-70% in game

I get the impression it freezes more around buildings possibly something to do with shadows loading?
heres the gpu usage (the freezes happen at the usage dips, same with cpu)
https://dl.dropbox.com/u/11391064/GPU%20USAGE.png

added

it does not happen as much in single player and will normally smooth out after a couple of minutes.

https://dl.dropbox.com/u/11391064/2013-03-09_00001.jpg
https://dl.dropbox.com/u/11391064/2013-03-09_00002.jpg

this is the building and angle where it happened