My girlfriend purchased a Prius C about 6 moths ago, and I purchased a Chevy Volt about 2 months ago, so here's my 2 cents worth.
First thing is the Volt doesn't get 60 miles on electric before kicking over to gas, except in idela conditions. Figure it will get around 40 miles on a charge, and probably less if you're driving at 75-80 most of the way. Also one you've used up the battery charge you're looking in the mid 30's to about 40 MPG on the gas. So the Volt is best at shorter trips, where the overall average between electric and gas use is high. An example would be if you you had a round trip of 80 mile and you got 40 on electric and 40 on gas, then your overall gas mileage would be 80 MPG But as you go beyond that the MPG numbers get lower, and with your round trip of approx 175 miles your average MPG will probably be in the low 40's. (One trip of 240 miles for me averaged about 41 MPG.)
For the Prius C my girlfriend averages about 50 MPG, so for longer trips her Prius gets better gas mileage than my Volt. So if you're doing daily long trips and it's gas savings you're looking for, the Prius is the better option. But that of course doesn't take into account ride quality, which the Volt definitely beats the Prius on.
Hope this helps.