Sorry to raise this thread from the dead.
North American Honda PCX 150 owners are regularly getting 90 MPG from the factory, that's without idle stop. The upcoming ADV 150 will have the same powertrain. A friend of mine who had one and driving on 90 km/h highways was regularly getting over 100 MPG.
It has a governed top speed of 104 km/h or 65 mph, the motor size and horsepower is similar to the Yamaha SMax 155 which is not governed and tops out at 120 km/h or 75 mph. When you go up a 6% grade however, the PCX is still doing very close to top speeed while the SMax drops down to about what the PCX is doing, so you're getting more consistent top speed with the PCX.
I don't know about the USA but the minimum speed on certain freeways where I am is 60 km/h. So it's freeway capable, but whether you're comfortable doing 100 km/h in a 100 zone where drivers are typically doing 110, 120, that's another story. I had a Honda CBR 125R before that had about the same performance as the PCX, and off peak it was ok, I was in the right lane and everyone can pass. Rush hour however, there I was in the HOV lane passing all those single occupant cars. It wasn't as efficient as the PCX but I was still doing 80 mpg on it without thinking of hypermiling.