Hi there.

I believe the M43 drives a specific current to the 12 leds, therefore runtime should not vary as a function of different leds. Having more leds producing a certain amount of light is more efficient than producing the same amount of light with less leds (of the same type).
So for runtimes you can google search for reviews, and those values should be the same if you have SST-20 leds.
I love my M43 very much!