Well I had a chance over the weekend to open up the car - 2000 miles, one oil change of break in - on a reasonably good stretch of reasonably flat highway and what an experience it was.
If its against forum rules to post details of illegal driving or anything, just yank the post.

We sent spotters both up-road and down-road to call on hand-helds if anybody was within a mile of where we were driving, but fortunately on a lonesome old country road nobody came during the 20 min or so that I was playing with the Z06.
I made a few runs, starting from 15mph or so on a roll to avoid clutch abuse. I ran the car through 2nd gear twice, then through 3rd gear, and then took a friend up to 150. I was pretty well scared by 140 but kept going just to hit the 150 point...
I'm sure this is old-news to most of you, but its news to me so i'll post it. The first two gears go by so fast you can hardly even scan the scenery. redline, shift, redline, shift. Third is a little less savage but not much, and by 4th you're going 120+ and still pressed in your seat, but the gear takes several seconds to finish so you have a chance to sort of relax. Except now you're going 150 which is scary in its own right.
The next time I ran it through 4th gear, which was ~160. I used the timer in the trip function to get a really poor estimate of how long it took... About 18 secs from 15-160 in those conditions. I didn't measure, but it couldn't have taken more than 1/2 mile, if even that.
And the next time I ran full-throttle through 4th and into 5th for a speed of about 170, and that was the fastest that I dared to go. It wasn't pulling nearly as hard in 5th as the lower gears and it would have taken a while and a long distance which I didn't have (I was running out of flat road and heading towards some hills) to approach top speed so...
Thats it. 170 or so. Maybe the fastest I'll ever drive unless i get a wild hair and rent a runway somewhere. But my car can clear the absolute ultimate top speed of my old Boxster S in less than 20 seconds, and thats all messed up. Its disorienting, frankly, to be in a car accelerating that hard.
It was AWESOME!!!