My testing of the lens shows the MFD to be 8.25 ft at 600mm, but that requires a manual override to get the last few inches... about 8.5ft w/ AF. Focus breathing at MFD is pretty significant with a resulting FOV of ~ 525mm. And it remains less than 600mm until ~ 30ft. FWIW, from what I have read the focus breathing is comparable to the other long zooms available.
The lens is also near perfectly parfocal; the focus does not shift notably when zooming to/from either extreme... which is very nice.
My comparison testing is relative to the 400/2.8 and the 120-300/2.8 w/ TC's as that is what I would otherwise use. I also have the lens set up to hyperactive/spastic (C1), slow/accurate (C2), and defaults (Off).
Compared to the 400/2.8 with the 1.4x the lens hunts more in low light/contrast situations. Set to C1 it will blow right past the point of focus repeatedly and very quickly (i.e. AF is very fast, but less accurate). Set to the minimums (C2) it hunts much less, but it is also much more accurate and slower (as expected). Defaults put it somewhere in between and somewhere close to the 400/2.8 + 1.4 in terms of speed/travel.
I suspect that the f/6.3 max aperture is just starting to vignette the f/5.6 AF points. But if you keep a more central composition using the f/8 AF points, or have good light/contrast, then the accuracy is greatly improved with much less hunting with any settings.
Resolution at 600/6.3 is very good... comparable to the 400/2.8 +1.4 @ f/5.6. But more importantly to me is that it is better than the 120-300/2.8 and 300/4 + 2x at any aperture. My best estimate is a resolution of 50-60lp/mm at 30ft. But that is for a recorded jpeg... reduced sharpening/contrast/etc settings, but some was still applied. I think at least the 40lp/mm from a raw file is quite probable from my copy (as tested/reported by lenstip.com).
So far I have not done any AF fine tuning w/ the dock... critical testing was done using CDAF on a tripod. But handheld results using AF have been equally impressive right out of the box w/o really trying hard.