Novice student in a modded e36 M3 sedan on Rs entered Turn 10 (high speed righty), got loose, overcorrected and swapped ends. He went off into the gravel backwards/sideways, slid 30ft, until the tires planted. The car then pitched 10ft into the air barrel rolled 3 times and landed on the passenger door on a tire wall. The M3 was completely destroyed (8" narrower and 6" taller than before!), but incredibly, both driver and instructor walked away without a scratch. The driver's door was flung off, all windows shattered and trunk and hood blew open in the roll.
I have also witnessed a brand new Boxter S go off in the very same spot last month and rolled onto its driver's door in the gravel.
I too have a Z3 (even with a roll bar/6 pt harness for autox) that I desperately wanted to do a school with, but after witnessing a roll over at 80-85mph, you definitely do not want to be in an open car. Rollovers happen much more frequently than you would believe...
Please be safe out there!