Much difference in ride quality of 17 vs 18?

Currently running factory 17" wheels on 2000 323Ci convertible and was considering going plus 1 (from 45 series to 40 series). With my stock sport suspension how much change will there be in ride quality? My stock sport suspension has all new shocks / struts and I have replaced all the worn parts. My car is more a cruiser so ride quality is important to me but I do love the look of the 18's.



Any help here is greatly appreciated.