I've been using a 2010 S/C as a daily driver for 3 months and my wife has a HSE. They difference in the ride is not so much harshness as it is a firmer ride in the S/C. Not in any way harsh. Definitely suitable as a daily driver. I found my BMW 545i with the sport package to have a much harsher ride than my S/C.
there is a big difference in the ride, yes the 20's are firmer on a good road - on a bad road they crash and bang !
it all depends where you live and what you want to do with the vehicle. If you want comfort, find a set of suitable 18" wheels and put 60 profile tyres on it - the ride is fantastic. That said I have 19" on mine...
Well I do have one with 19s and one with 20's, that's what I was saying. Now one has the HSE suspension and one has the S/C suspension so that makes it less than apples to apples but even so I have never experienced anything like crashing over harsh roads, my 2010 S/C is pretty darn smooth compared to many cars I have owned. I"d be surprised if anyone found it too harsh a ride. And no you cannot fit anything less than 20's on the 2010 S/C because of the big brakes.