You still have this problem? The reason I ask is because I came across this thread having my own stuttering problem, and I managed to fix it after a few hours.
My fix: Disabling chat logging. What happened was that now that I got my 3rd Tier1 henchman, my combat log suddenly grew huge. I kept on thinking it was a problem with the particle physics, but this thread prompted me to do a fragmentation analysis. The result? 6 MB chat log with 500 fragments. Once I disabled chat logging, everything was fine.
I dunno if this would help you, because I don't know your exact situation (when it occurs, etc.). For me everything made sense because I would only stutter during heavy combat situations.
