How's the car at 70-80mph?

I made almost the same move you did, except my Jetta had the 1.8t engine. So obviously the Prius isn't nearly as fast as my Jetta was, but you should find it comprable to yours.

You will not find the braking or handling to be comprable. It handles and stops adequately, but it doesn't inspire that feeling of supreme confidence that the Jetta did.

 

i didnt get to 90 on my maiden voyage home, but i will say i hit 75 before cutting it back (was in a 60 mph zone) and was shocked that i was going that fast. without feeling a shift from low to high, the acelleration is very deceptive.

 

Another data point: went to Bellingham the other day, driving an average of ~72 MPH. Total average for trip was 48 MPG.