The heads are about the same diameter, so unless one is driving the LED harder, I don't know what would be causing that big a difference. I wouldn't trust the numbers, they are probably just copied from some other specs.
The heads are the same diameter, but the reflector on the C5 should be much deeper considering the difference in body length - 180MM to 156MM. That should give it better throw.
I might try a C9, the driver and modes in the KD version of the C8 work as expected. Anyone else surprised @ the brightness of the low mode considering the tail pull on these? PWM + Current combo?
I guess the light I would probably wait to see how it works out, and then get instead, is an XM-L recoil. The C8 might be the last flashlight I need for a long time, if the low mode has good life on it.