You won't regret it!

That diesel is wonderful to drive. The sport package is comprised of more than the 20" wheels though. The trim around the grills, the trim around the windows, the suspension setup, etc... I would go with the standard sports package (which I think has 19" wheels), then buy the 20" for the good looking part. At least this way, you get the benefits of the sport package, and still have 19's for winter...
Either way, still gonna be a nice ride.