Hi Dan - thanks for the bump, I’ll check this now and see if I can see the same thing.
Hm - here, opening the same fairly complicated V5 model in all wireframe and running SetDisplayMode Shaded rings up at 15 seconds in both V5 and V6. I’m guessing not, but just in case, are the models using any fancy mesh modifiers like edge softening or displacement?
Another example here: S-L-O-W Meshing
https://mcneel.myjetbrains.com/youtrack/issue/RH-45753
-Pascal