Question about Arctic Z2

I have 2 x ASUS VE278s, each weighing 5.1kg. I am basically satisfied with the support arm system. I always have to adjust the screens again because they fold down.
Your plan with the 7.5kg monitors will certainly hold. But it's possible that you'll have the same problem with the adjustment.

I have two older 24s with a decent edge hanging on them. It works quite well with them and they are probably about the same as your 27s.
What I don't find optimal about the mount is the screw on the vertical bar, I have a bit of air there and therefore the monitors (I don't have them in the middle, but offset to the right) get a bit tilted. But that has been corrected...