(all opinions based on 2.8 only)
Corners soft, lots of hard vignetting in corners.
AF speed is actually VERY fast almost right there with the mk2
distortion is high imho
OS seems non existent although me sitting controlled I get about 2.5-3 stops during images but viewfinder/video doesn't show much if any affect maybe 1-2 stops
weight for the size of it it's pretty heavy. I mean the 85A is heavier by 4oz but the size of the 85A is huge so it just "feels" lighter
balance is ok on 5D4... slightly front heavy, I prefer the mk2 balance as it's just right
focusing is dead silent and super smooth... doesn't even get picked up on the internal mic which is amazing
center sharpness is outstanding and matches the mk2 but the sharpness falls off quick and extreme corners are ugly
found a bad piece of lint in a brand new lens right in the center of the element inside... no likey
lens weighs 36.08oz w/ no caps and 37.38oz w/ hood on no caps
gasket is nice like any other L gasket on the rear
size is around same as the Tamron VC model
build is very nice... zoom ring is very smooth yet firm just right
ghosting if focus is missed slightly... under brighter conditions at 70mm 2.8
ZERO options in dock menu to adjust OS!!! None... none existent
bokeh and colors are typical ART... very good.
Mind you I had owned two copies of the Tamron VC version and used that lens for 3 years... the VC on that lens is way better already and the new G2 is suppose to have a VC upgrade to 5 stops. Honestly the sharpness I can't really judge well... I've been spoiled with really good primes and I'm use to prime corners. The Mk2 appears to have strong sharpness falloff on the TDP test charts so I bet anything it's probably pretty close. AF is really fast I'm impressed... much faster than the Tamron.. this thing snaps right to it but I still think the mk2 has the edge. I bought this lens to have a main video lens/vacation lens. I demand GOOD OS/IS/VC. I'm 85% sure I'm sending this back and getting the Tamron G2 lens for this need.
This was with about 1.5hours of messing around w/ the lens and 138 images taken.
EDIT: Just wanted to add my comment from my post below... you guys KNOW I am a Sigma fanboy so for me to post this is 100% unbiased facts by me... Unless Sigma comes out with OS adjustments via dock to lock it better I'll pass.