Normally, when folks go to larger wheels, they also go to smaller sidewalls. The 70 series sidewalls give way to 65 or 60 series sidewalls when the 15" or 16" tires are selected, respectively.

I cannot feel any difference in ride quality between the 70 series sidewalls on the SD and the 65 series sidewalls on the SDL. Both of them have a relatively poor ride and find every slight crack in the pavement. The SDL is actually better than the SD due to the tires and the longer wheelbase.

Naturally, if you carry this to the extreme, I'd expect a decrease in ride quality if you went from a 70 series to a 55 series. That's just too dramatic to overlook.