VERY nice work
Enough so to get me out of hiding, LOL!
Your custom block uses one of several design concepts I've been toying with to improve block performance in general (the "split path" concept). Really good to see theory and reality correlating so well
I would be curious how the copper spiral would perform if it's base was milled down to 3.5mm, the same as the custom block's base. Might we convince you to do that test? (with the different base thicknesses, it doesn't give the best comparison regarding the channel designs).
The other thing is that I am a bit surprised that the water temp at the outlet is exactly the same for all but one of the blocks, considering that you have a 4 degree C temp difference of the core for the top 2 and bottom 2. Are you sure that you have the thermocouple inserted so that it sits in the center of the water flow and that it isn't touching the copper pipe it's inserted through the wall of? You might also want to put a piece of foam insulation around the pipe and hose where the water temp sensor is to try to isolate it thermally from the ambient environment.
And of course, it would be great to see some tests with a higher heat source (100W to 120W range) and possibly even a set with a pelt combo so the heat input is in the 200W to 300W range. In general it provides very useful data and insight into a cooling combo to perform th testing at different Q levels.
Again, GREAT work