Someone already mentioned antivirus, I had pretty bad stutter in some games every 5 seconds because of that.
Or, you're just sensitive to stutter. When I was experimenting with my crt at high hz. I couldn't get mouse movement smooth in bf3, strafing was. Solution was to overclock my mouse from 125 to 500 hz. Then I just bought a 1000hz mouse. You say you have tried 2 gaming mice, so you probably already have a high hz mouse, but the symptoms are the same, so I mention it.
The only way for me to get battlefield 3 perfectly smooth btw was to run the ingame fps limiter AND vsync, fps limiter on exactly the screen frequency.
Same in assetto corsa, ingame fps limiter and vsync.
It makes sense if you think about it, if the game (due to the limiter) starts a frame every X ms and the screen matches it at the same frequency in the right order it has to be smooth, provided the mouse input isn't jittery of course.
Of course you'll want to make sure settings are decently low so you dont drop and you'll want to prevent the gpu from clocking back (in nvidia control panel there's a "prefer max performance" option somewhere). I run a static overclock and I've turned most powersaving off (only have C1 on), but modern cpu's have powersaving that sometimes get in the way of games, could turn them off for testing purposes, setting windows to high performance in the power options also helps (can use it to trick the i5-750 in using the 21 Multi all the time), there's also a small executable around called settimerresolution, saw a video of it improving crysis 3.
Ideally you'll want to have the screen and the mouse frequency match as well , but with 1000Hz mice around that shouldn't be noticable.