Upload & Sell: On
Well, I went out and got a second 5D3 body, and I can definitely say that both are exhibiting the same thing. The second body tested almost exactly inline with my original body (slightly different exact numbers, but same overall performance).
I got around to testing this today. On my 5DM3 + 50mm f/1.4 at a focus distance of 1600mm (32x) using indirect outdoor daytime natural lighting, MF once in LV and not altered between targets I get the following results from the ML DotTune (3 runs with each target):
Bob Atkin's target, focus on the intersection of the 2.2 horz/vert lines: 3,3,4
jmvdigital's horz+vert target at intersection of cluster of lines: 4,4,4
jmvdigital's checkerboard target: 1,2,2
Of all the targets the best in terms of AF confirmation consistency and speed was jmvdigital's horz+vert target, followed closely by the Atkin's target. The worst by far was the checkerboard target - I saw some huge individual AF confirmation outliers with that, although they averaged out with the ML Dot Tune. I didn't try the vert vs horz because in practice I would never rely on only one direction of detail for tuning anyway, even on a cross-point AF sensor.