I have taken several long trips over 1000 miles on my Silver Wing. It is 600 cc
But I have traveled with friends riding 400 cc and 500 cc maxi scooters. The 400 cc performed as well as my 600 on the roads. One could feel the power was stronger in the 600 however on freeway, highway or byway we all road at posted speeds with no one left behind.
Here's a Piaggio X-9 500cc and my Silver Wing