0-60 is more power/weight, 60-150mph is more power/aero drag.

The V8 should be more in its element on the highway from about triple digits on. In that range huge amounts of revs + clutchslip will not help. (as they would off the line)

If the bimwad was already getting ready to pass he likely already had the "passing gear" in. You had to punch the gas and wait for the tranny/motor to get their act together. That alone could make the E430 seem less capable than it was. Plus if he was carrying more speed than you before you punched it. It takes tons more power to overcome a shift delay and/or speed defeceit. Also, acceleration from higher speeds is less dramatic than from lower speeds. This could make a big difference seem smaller. Put your foot on the gas from 15mph and notice how quickly you feel an effect. Put your foot in it at 115mph and try the same thing.

That said, (as has been noted above) you still have em "dead-er than hell" when it comes to the view through the mirror.

Hope this helps...Lee