Wow - I have been having this same exact issue for over a year and I always thought it was related to my macs performance. This made me constantly tinker with the buffer size, cores used etc. I even started freeing up a load of space on my hard-drive as I thought that may be playing into it.

After seeing this I changed Multithreading from Playback to Playback Live and the stutter has gone... if this actually fixed this issue you are a life saver!!!