Sorry - can't resist.... :laughing: I thought size didn't matter......
Anyway - That is an awesome thread on the M6 that I have read about 3-4 times and learned a lot about the options.
I don't have the M4 or the M6 personally because I wanted to avoid using that many primaries. I do have a FM Megallenium and a FM 2x26500 M head light both with KT4 heads.
A few things to note - not every KT4 head is the same. Of 2 KT4 heads one was definitely more throw and one was more flood.
I've run MN16 on 2x26500 lions and it is pretty stellar. Moving up to a MN21 is much brighter. Going with some custom WA1111, WA1185, FM1909 and the spread of LF bulbs my results are interesting. With the KT4 head there is definitely difference in brightness between different setups but there is more of an effect on the size of the spot as brightness goes up. As the filaments get bigger so does the size of the spot - so brighter bulb doesn't always correlate to more throw.