On my 1984, from South Dakota to Nevada, I averaged about 85 mph. I think I was tripple digit in the Colorado mountains, but I could not look down at the speedo; I was way too busy looking for the next curve and grinning from ear to ear.
Like others have said, these girls like to rev high and ride fast. Adjust it so you are comfortable on it, and get some good tires, then go play and see what your particular bike likes to do best. Both of mine love mountains and fresh air.