Having both the 70-200 f/2.8 L IS Mark II and the 70-200 f/4 L IS, I would certainly like to do the "human test" on these two new offerings.
Like others have said, and I can agree, that the 70-200 f/2.8 L IS Mark II still sooooooooo good. Really tough to beat. But still Heavy...........
Regarding the f/4 L IS Mark II, that would be the one I would like to try. Improved IS, sharpness and colors that compare to my newer 16-35 f/4 L IS and 24-70 f/4 IS. Not that my f/4 L IS Version 1 sticks out like a sore thumb. What really has my interest or concern would be the over all weight and how this new Shape, 72 mm, feels on the camera body compared to my 67mm f/4 L IS Version 1.
Again the old "Human Test" would answer that.
The new f/4 L IS Mark II just may have me in the market. As I leave my f/2.8 L IS Mark II "state side" in favor of my smaller lighter, f/4 L IS, my "Greek Trilogy of the Canon f/4 L IS, (16-35 f/4 L IS, 24-70 f/4 L IS and 70-200 f/4 L IS) for Euroean travel, may get a new addition to the family.
We shall see............
Canon 5D Mark III (x2), BG-E11 Grips, 7D (x2) BG-E7 Grips, Canon Lenses 16-35 f/4 L IS, 17-40 f/4 L, 24-70 f/4 L IS, 24-105 f/4 L IS, 70-200 f/2.8 L IS II, 70-200 f/4 L IS, 100-400 f/4.5-5.6 L IS, TS-E 24 f/3.5 L II, 100 f/2.8 L Macro IS, 10-22 f3.5-4.5, 17-55 f/2.8 L IS, 50 f/1.4, 85 f/1.8, Canon 1.4 Extender III, 5 Canon 600 EX-RT, 2 Canon ST-E3 Transmitters, Canon Pixma PRO-10 Printer