FWIW, I'd tend to argue that 'machine gun' cannons should do at least somewhat more DPS, due to the fact that it takes more precision to maintain a tracking shot over time(especially if the cannon has a lower-end shot velocity) than to line up a snap shot and fire a single salvo of high single-shot power cannon.
It depends on what you intend to shoot it at, I suppose. For an example, I think the Balor's fun for the dakka, but if I'm trying to kill a Fury-AI Dragon, which I may only see for a second or two at a time as it continually circles me, I'd rather blast it with a full salvo of Prom-S than try to keep it in the exact same spot in a cycle-stream.
Cont'd: Also, maintaining a tracking shot over time forces a somewhat inflexible flight pattern(thinking particularly if you're under fire), as you basically have to follow your opponent perfectly in order to do the same damage over time as the single-shot power cannon can, though the latter would have the option of jinking in between shots without worrying about affecting its damage rate very much.