The ride wont change much, however, the car is probably running on Bridgestone RE040 tires which may have an impact on the ride quality. There isnt much you can do about the suspension however.
As for the seats, I think they feel different for everyone. Personally, the seats fit me like a glove and im 6 ft 1. However, there have been a few people complaining that the seats are too small, it all does depend on the build of the person.
The GS450h is awesome and does not feel cumbersome at all. Its planted and is a quality piece of kit!