Car? Nothing much, maybe 120 mph when I was younger. But a buddy and I picked up a Piper Cheyenne in Lakeland, Florida, back in '88 for a delivery flight to Vegas. Fibbed to ATC that we were going to put down for a rest at a little airport in New Mexico, and then beat up the desert floor at about 350 kts, maybe 100 feet off the deck, maximum. Equates to about 650 kmh, 400 mph. Really feel the speed at that altitude. That was one of my last times in the left seat, medical took that away not long after.