the v8 doesn't have as clean an aerodynamic shape as the regular 5000/100 models. it's Cd is rated as 0.34, vs the more typical 0.29-0.31 of most of the post aero audis. that would count against it for super high speeds. i'll bet that all that extra area devoted to the huge radiators, the wheel arches and fatter tires all contribute to it. eliot