Does your game stutter in campaign and in custom battles? I found that I can run 250*250 custom battles with no stuttering but as soon as I engage 10 looters in a campaign I get a stutter every few (10-20) seconds.
Maybe the campaign blocks more ram because it keeps the map etc. loaded or maybe it is some kind of campaign specific stuff like the level system that blocks stuff... ?
Same issue for me. 200v200 custom battles run fine, but if I take on 5 looters on my own in campaign the lag is basically unplayable.
I have similar specs as op but with a GTX 1060.