I've been getting massive game-killing frame-rate stutters of around 2-3 fps for 10 seconds at a time, since the last update which corresponded with a Windows Update so I didn't know what to blame. I tried updated graphics drivers, restoring PC to clean install, everything. Nothing worked. Happened even if all graphics settings in the game were turned off.
I finally noticed that when the stutters were happening my CPU speed was getting massively throttled (it's a laptop, plugged in). It would normally run at 135% or so, and during the stutters it would drop to 16% for like 10 seconds, and then go back to normal. I ended up disabling throttling using registry setting. I'll let you look up how to do that–I don't want to be responsible for messing up your stuff, e.g. you don't want your laptop to overheat. Mine seems fine now–the fan speed goes up and down as necessary so I don't seem to have any run-away heat condition with throttling disabled.