I'll trade you my '05 Prius with 120k miles for your Volt.
A manual gen1 Insight can't be touched on the highway; it'll easily beat a Prius by a good 10-15MPG at any given speed. City mileage is all up to you, but it should still beat a Prius given similar driving styles. Being able to still drive it with a dead/dying battery is also a plus (Prius is big metal brick with a dead HV battery). Both are great cars, though.