I have followed my GF at 50-52 mph on my GPS, on a down hill she was on her 49cc chinese scooter and I was on my V-strom, I have ridden her scooter only once and it was downright scary when the speed gets to 35-40mph
my first bike, a 1966 Honda Super90 blew the engine when I was going down a steep hill 80mph, my next bike, a Honda CB125S was only capable of 65mph max