my search abilities fail me, but sometime ago (in a universe far, far away) we had a thread on "high speed" autox's (if someones finds it please link it )
I got to attend another a weekend ago, to say the least these are very fun. They are not w/o risk, thus SCCA's recommendation to keep Solo events @ 65mph and under. SCCA does have a new "option" a faster autox format (w/ more safety equipment required) that allows speeds up to 95 mph (same SOLO classing). There were a couple of minor offs (automatic DNF for that run), one that was probably a little more than minor- no injuries, but broke two tire beads on one side of the car., but all in all laid out nicely so you could push the car prety hard.
here's the site- the left side (infeild) had a somewhat traditional autox start/finish setup here- much of the remainder of the track was left as is- the long straight had some offsets and some slaloms in in it to scrub some speed. I was into 3rd gear twice in the course (2nd tops out at ~ 70 mph), probably in the 85-90ish mph range (never looked down )
a nice way to get a track day like feel w/o having to go full out