Without knowing your driving habits and/or the type of roads you frequent (hilly, flat, twisty, straight, high speed, low speed, open roads or constant start/stop) it is impossible to say.
Ideal gas mileage would be obtained if you were able to maintain a constant speed of 55 mph (per gov tests) in a straight line with no altitude changes. Anything higher will affect mpg as well as anything else that deviates from the tests. Testing the limits of your bike will affect mpg the most so after the new bike feel wears off or you have a reason to conserve fuel your mpg will increase.
Retired USAF, IYAAYAS!
2008 V-Star 1100 Custom Bobber project
2011 Crimson XR with Forged Highway Bars / Hard Bags / Passenger Backrest, Ness parts including Smooth Layback Plate Frame/Mount / Rad 3 Mirror / deep cut grips / drivers floorboards /shifter peg / brake peg / passenger pegs. Witchdoctor black rack, Lloydz filter / timing wheel / VFC III, 7Jurock windshield, Drag Specialties seat.