Currently, PC users can change how many processors are allocated to KeyShot. Do this by going into your processes tab on the task manager (ctrl+alt+del). Right click on the KeyShot process and then "set affinity". In my case I can un-check 1 of 4 CPUs and regain performance for non-keyshot programs. This works for both realtime and rendering.
Wouldn't it be better if we had a quick selection in KeyShot for this?