9 out of 10 points and recommended
Just a couple of additions:reviewed July 1st, 2016 (purchased for $1,500)
The focus ring on my 100-400mm is IMO aluminum. Cold metal anyway, not warm plastic.
After I got it I set up a simple comparison test shooting the AF resolution target in the center of the frame with three lenses: 14-140 MK II, 100-300, and 100-400. I tested at 100, 140, and 300. Results were surprisingly close and, more surprise, the 12-140 seemed to be slightly softer than the other two.
I'll be taking the 100-400 to Tanzania this month for a 3 week chase of the Great Migration. I'm really looking forward to seeing how it performs. That said, I will probably sell it when I return. It's so big and heavy that, with a GX8, it really destroys my M43 objective of small and light. Plus the 400mm end is not one that I use on a regular basis.