As to the upgrade on the Springs, I am waiting for warmer weather to judge. In the past few days it's handled pretty well, but nothing like my 2005 330xi. So, in the spring, I may upgrade the springs! The cost was just over $3200 because of a 10% discount my BMW dealer was offering - through the end of the year. The transition took all of a morning. The pure power is amazing and the P-Zeros run-flats are definitely getting a workout.