Yes, close all other apps. Some browsers generally use a ridiculous amount of memory and the web pages you have open can also have an affect on system performance. What about stuff running in the background? Anything significant will often have an icon in the top right corner of the menu bar.
I closed all apps and tried again. Sadly, the problem still persists. More specifically, the camera stutters a lot and also feels slower to move around, especially when hosting parties or when speeding the game up. However, the game still loads really really fast for me, which seems really strange considering the other issues. Another observation I've made is that my computer doesn't heat up as much as it used to when playing the game, however I also haven't been playing for long sessions as I did before, so take this with a grain of salt.
Does this happen when playing in windowed mode and fullscreen? Or just one? When in fullscreen do you have Game Mode enabled? If so, does it happen when it is disabled?
Could you set up a new user account on your Mac and play the game in that account to see if the performance is still slow?
