Just got back from an Audi Chicagoland autocross event at the Tire Rack headquarters. They have a newly redone test track that was just phenomenal...a mini-road course. This was my first event of the season and first time on Bridgestone RE-11s. Let me say this: best tire I've ever driven. They were flawless, and I finished 1st in class and 2nd overall (beaten only by a 911 with R-compounds).
This course was just ideal for the Z and the RE-11s are worth every penny.
FWIW, people have complained of bogging or throttle lag when they stomp the accelerator. I was having a lot of issues in my early runs with the car just falling on its face off the line at the start. The solution was just more RPMs for the launch...too little she bogs, a tad more revs and she's a jackrabbit.