Just as a side note I was checking ROF last night.
For the Ki61:
500 12.7mm: 17 s = ~ 882 rpm
240 20mm: 9 s = ~ 800 rpm
For the Ki84 (because its guns are in the nose, sync'd)
700 rds 12.7mm firing time: 22 s = ~ 954 rpm
300 rds 20mm firing time: 11 s = ~ 818 rpm
For the C2, because that's what I think of when I think of slow lumbering sync'd 12.7mm guns
12.7mm firing time: 35 s = ~ 634 rpm
7mm firing time: 38 s = ~ 789 rpm
For comparison I think unsync'd .50cal go 800 rpm.
EDIT: The US .50cal is 1.23x more powerful than the Breda SAFAT according to this:
http://trainers.hitechcreations.com/guns/guns.htm