Hi Clivey, I guess I don't completely understand what you said, but seems like regular alkalines good for longer reliability in the triggers and NiMH would be more power in the flashes?
Sorry - I mis-typed. Here are the corrected figures:
YN-622C low-power threshhold = 2.2 volts.
Nominal NiMH - 1.2 volts, x2 = 2.4 volts.
You are on the way out before you start.
Only 0.2 of a volt to start with, compared to 0.8.
NiMH can deliver to the flash the current needed to get a fast recharge.