All depens though.
For instans here in NYC the regular fuel is 2.79 & premium is 2.99 which is only 20 cents more.
If you do the maths is only $ 4,50 extra for the premium.
When i used the regular fuel i was getting 'bout 16 MPG but with premium my horse is recording 22 MPG (highway) which is 6 more miles.
Of course traffic conditions & drivings manners apply