the 600 engine is vibration free and deserves easily the tonup-sticker, even with a passenger. the 500 however, did 80 top when i bought it, and after a lot of succesfull and even more failing alterations for racing, it did 100+ on the track. For the mickey-mouse-tracks in the villages that's fine, but for a real track it is horrible. When it was build back for street use, it was a shaking and loud machine, but I could cruise it 80mph. The difference between the two engines is huge, in performance and in smoothness. I never liked this 500 engine with a sidecar, but the 600 is made for the job... And on the back roads (or the applecross roads) it is a twin-beater: much lighter and more power then some rapides...