I installed the HR 24mm rear bar on my 2010 sport, with the stiffest setting. It helps body roll, but not enough. I then replaced it with the B&H 27mm, also set to the stiffest setting. The B&H has better roll-control, but somewhat more would not hurt. I would go for the special H&R "Time Attack" version that AWE Tuning had made for them, which is 28mm.
The ride quality was hardly degraded by the H&R 24mm, or B&H 27mm. I would rate the ride changes as almost none. I put the H&R 24mm onto my wifes 2012, and she has not noticed (or mentioned) anything different concerning the ride comfort.