OK so regarding the mouse, NVidia FastSync + 60 FPS lock does wonders for the feel of it. It's perfectly tolerable right now. V-sync and plunging framerates seem to be the culprit here, as expected.
In my case, fastsync causes stuttering while in-game vsync setting does not. I have a 60FPS lock in both scenarios. Sounds like another game where performance is all over the place on different hardware configs.