I dont know anything about the Mitsubishi coils, as you say they have to be fairly quick charging for that RPM, but I've no idea how much spark energy is needed to ignite a rotary engine.
I always point 4A-GE installs towards the Mitsubishi EVO4 coil packs, Sweeps took a punt at using the EVO5 coils:
These seem to work quite well at 2.5ms and a lot of these engines see 9500rpm on them.
FWIW I have a pair of EVO4 coils that will be available after I get the MSD EDIS coils