I wanted an all season tire so I went with the AS/3s. The 370 sat in the garage way too often last winter due to the cold, and since putting on the AS/3s, I've been able to drive it more and no more "chirping" when cold and I really don't think you give up that much with them on the street. They were top rated A/S ultra high performance tire by Tire Rack.
http://www.tirerack.com/tires/tests/...y.jsp?ttid=177
No regrets whatsover.
I don't believe the Driveguards are available for the Z w/Sport Pkg. tire sizes.