Top Speed of motorized scooters?

I am looking at purchasing a vehicle with better gas milage. I have seen many people driving around on scooters these days and was wondering if anyone knew what the top speed of one was.

I have to get on the highway for about 15 miles on my commute and didn't know if this was even legal and if it was how fast do they go.

50cc scooter top speed is 30 mph
125 cc scooter top speed is 50 mph
250 cc scooter top speed is 70 mph
400 cc scooter top speed is 90 mph
650 cc scooter top speed is 110 mph

for high speed highways at a 65 mph speed limit I would go with the 400 cc, for 55 mph highways the 250cc will work.
you need the 400cc for quick acceleration and speed when merging on to traffic on exit ramps, a 250 cc scooter doesn't have the quick acceleration.
the 250cc scooter can reach a 70 mph top speed but it might take almost a mile to reach that speed.
I highly suggest the Suzuki Burgman 400, or the Honda Silver Wing, or the Yamaha Majesty