I actually love the look of that tire on my car. I have my spare set of rims powdercoated black so it looks pretty tuff. I don't think that it affected the speedo all that much, at least not up to 80. email me if you want to see pics of the tires on the rims/car.
My other ride is a helicopter, it has 420 shaft HP derated down to 317 by the tranny (thats all it can take)...I'd rather take the Z.