I test drove both and didn't notice any increase in harshness. The only time I felt really harsh roads was on the cobblestones in Verona, Italy. Any car will feel harsh on that. On any other roads though, all 3series seems to dampen the bumps. I can honestly say i've never felt anything like it on any other car (and I've test driven a LOT). ZHP is probably fine, but go test drive it on some normal roads out there.
Proud owner of an '05 Silver Gray
330i ZHP with Natural Brown