Microstutters with Hyper Threading on.

[keef]

Ah, I finally pinpointed the problem and thought I'd share. In the bios are two settings. "CPU C3 Report" and "CPU C6 Report". By simply turning off both, I can now leave hyperthreading on with no issues.

There is no discernible difference between having HT on or off, performance wise. Another thing that was necessary for smoothness was to turn on vsync in Dolphin.