Did you try with Vsync disabled, as in certain games thats exactly what i got, Just Cause 2 being the worst in that moving in a straight line everything was fine but turning produced a lot of slowdown/stutter, without vsync the problem just wasn't there, turn it off in game and remember to check the CCC just incase you have vsync forced in there aswell. I'd also try with just vsync enabled in game, and vsync forced from the control panel.
THeres certainly some oddities lately I'm finding, Nvidia/AMD and various setups have strange stuttering no ones really found a cause of, while Vsync worked for me in Just Cause, other games can have a little of the same issue while plenty have entirely no issues.