[Perfectlap]

I think most Stadium sized Lot autoX events (that are well configured) go up to 70-80mph. Nothing unusual.
Personally, I wouldn't attend one that was slower. I tried that once with BMW club, small industrial parking lot, sea of tightly spaced cones...my tires were screeching the whole time. Not fun...
At the other extreme, we've had very very fast courses where 3rd gear and 90+mph was reached and imo that's not really an autocross anymore, not to mention the lap was done in 45 seconds and the whole event ended 20 minutes early. You need a balance.