The reason the for the difference I think is the weight of the car. THe Z8 is 4320lbs, compared to the MZ3 which is probably less than 3200lbs. This past weekend i visited some family in Atlanta, at our labor day weekend party a family friend brought his new Z8. The car had only 320 miles on it. I drove it for 20 miles or so. Anyway, the car is beautiful, but one thing i did notice is that it did feel quite heavy, when compared to what my M3 feels like. With respect to your question about a hard top, my friend told me he drove the car home from Spartanburg, SC to atlanta GA in Heavy thunderstorms, and he mentioned the car performed perfectly without any noise from the heavy rain. Enjoy the car, alex