If you mean, how's the ride quality w/ the SPL rods, then the answer is 'just fine'.
The only time quality suffers is when I hit something on the road like a small imperfection or the drunk bumps...is just sounds and feels like something much worse just happened.
As far as bushing stiffness, how I understand it, all poly-bushings can potentially cause the problem. They don't give the play the stock bushings or the heim joints do.