Can a 580EX II handle 10 fps from a 1D Mark IV on quick flash?

C.Fn III-16 adjusts the fps rate on my 1D Mark III. I can't see why Canon would remove that functionality from the Mark IV. The Custom Function is not very intuitive but it works. Both the High and Low speed settings can be adjusted by first setting the desired FPS in the Register box.

I've shot both indoor and outdoor track & field at 6 fps with a 580EX II for fill flash and I didn't get dark frames. My flash was set at no more than 1/4 power and was powered by a JackRabbitPack II battery. You certainly can't shoot like that at full flash power....the thermal protection circuit will shut down the flash if you shoot too many frames without allowing the flash to cool.

I never owned a III, IIN and IV don't seem to have that functionality. I know CFIII-16 on The IV is now AF Orientation. I was just playing with it, last week.

If I can get 1/4 power at 6 fps I'll be very happy.

I take it back, actually opened the manual and it is in there. CFIII-18 now.

Disable: Continuous shooting will be enabled:
H - Approx. 10 fps,
L - Approx. 3 fps
Enable: The continuous shooting speed set with [Register] will be enabled.
Register: H can be set within 2 fps to 10 fps, and L can be set
within 1 fps to 9 fps. After entering the settings, select [Apply].

Ha-ha, I was just about to suggest some reading of the manual, but you found it out yourself.