Thanks again for sharing this stuff
IMO, the 12mm/15mm setup shown here looks much better balanced than the 20mm/20mm on the YMB M3 in the other thread.
So the difference between M3 and M4 seems to be in the neighborhhod of 50lb as advertised by BMW at launch (+17lb difference here -50lb ½ tank of fuel -15lb CCB = -48lb)