Do to the editor preferences not supporting binding of the same key to start and stop simulation (play, stop) which seems like a reasonable thing to me, I would request a new editor pref for Toggle Start/Stop Simulation much like the existing Toggle Play/Resume.
If this were available id use F5 for it, as an example. The main thing though, is i cannot have the editor consuming escape key presses as this is a very very important key for any game with any sort of ui or cancelable actions. And, id really rather not have to remember to like … press SHIFT+F5 to stop it or something.