Well there was that one time I facerolled 4 mechs at once with the Demo prime but overheated before I could kill the fifth one...
And yes, I have overheated a few times, but the pauses to keep from overheating is what keeps the Demo prime from being insane, if you can just fire constantly all day it will be a pain in the ass to deal with, (it already is but not annoyingly so). I will hardly see a difference in the AC10, but AC20 is another story.
As it is the overheating is the only thing that slows me down when I'm in a Demo prime, without it I'm sort of afraid it will be easy mode.