Ummmmm, good point!
In reality, bone stock I got 22 MPG driving all highway, driver only.
But best guess ....the absolute best you can expect is "about" 19, with most I'd say around 15, some report 11 MPG. That's kinda the range with many having larger tires and/or rims, roof racks, baskets... Just some ballparks!
Some report better mileage with premium fuel, some don't.