Just out of interest, is the rear width of the 18's 265 instead of 295? I find that it is easy enough to lose traction on the rear in first gear (coming out of corners) with 295. Guess you will have to be a lot more careful if it is 265 then?

Btw, the tyre pressure makes a huge differece in the ride quality on the 19's. When I drop the pressure to the minimum recommended by Porsche, the ride was much more acceptable.