I LOVE! my P85+ and it's 21"ers. I prefer a firmer ride. So I really can't say much about harshness. From my POV, she is smooth as silk. The staggered tires can be a hassle. I did swap out my Michelin PS2s for Hankooks, which are wearing much better. Though the rears do give up a little bit of grip. I love the RWD. I love the air suspension because I live in the mountains with many areas where I do need to raise it to get in drives, etc.
I have been told that it does have more road noise than the 19"s. But I have not had the chance to compare. I expect that at some point in the future, I will probably do a DynaMat soundproofing just for Sh-ts and giggles. I do hear road noise; perhaps more than I would like. But the MS is, by far, the quietest car I have owned. And for a 4,600 pound beast, she handles really well. Always firmly planted.
Road noise is really tough to quell. Dynamat, in my opinion, does very little based on my experience (did a lot on my 2005 GTO). The mass loaded vinyl (i.e. heavy vinyly suspended on foam)' does better at blocking noise, but you do tend to have to put it everywhere. I've never done wheel wells and have occassionally wondered if that would make a material difference. Quieter tires seem to be the "best" solution by far...speaking of which, what size Hankooks did you install CHG? Did you go bigger or smaller than the stock size? Was there a change in noise level vs. the PS2s?