OK, gang, I have a little more performance data on the 4.6is S3. Using some advice from others regarding launching (see
http://www.xoutpost.com/x5-e53-forum/...ch-e53-x5.html ), I did a few "brake launches" (holding down the brake when pressing the gas pedal a little) with transmission in "S" mode, and got a 0-60 time of 5.2 seconds, or .2 faster than my best time just flooring it without the brake launch (timed with G-Tech ProRR).
5.2 is the same 0-60 time as the Cayenne Turbo, which jives with my experience test-driving a Cayenne Turbo (it felt fast, but no more so than my S3 4.6is)! Of course, the NEW Cayenne Turbo S now has 520hp and does 0-60 in 4.8 seconds, and I don't think I'm ever going to get my X5 to do THAT, but still...the Cayenne will never look as good as an X5, either!
As for gas mileage, after half a dozen tankfulls, my city driving is consistently coming in at 10mpg. That's not the cars fault; it's my tendency to keep it in "S" or shift manually (it's just too damned fun!). Still no stats for highway driving, but I expect that will be little different than stock, since it would be mostly in 5th gear, and supposedly the supercharger doesn't directly hurt gas mileage much.