I have a 4.4i SP with the 19's and have driven plenty of Xs in all iterations. I once wrote a detailed description comparing back to back differences between a 4.4i non-SP vs. SP. My estimate was a 15% stiffer ride in the SP. As with all things in life, there are compromises. If you want a vehicle that performs exceptionally well on-road, then you have to give up some level of comfort. I would not go as far to say that it's a harsh ride at all. Then again, my previous cars had either the standard sports suspension or modified using Bilstein Sport shocks with stiffer and lower springs. So my perception of the X in SP guise is comfortable. There is no clear cut answer on what determines harshness much like how much power is too much? One thing is for certain and that is the 19's will ride stiffer than a smaller diameter wheel.