Fuel mileage depends how you ride...on my normally aspirated, slightly richened, carbed '04 Sportster...with straight pipes (with 1 3/4" with 12" baffles) all highway mileage...49 mpg best, a mixture of city and highway like on vacation around 45 mpg, only city and short trips to work, 35 mpg. So yes, 4.5 gals is most available stock...so you can do the math for expected range. EFI complicates things, as you would use a fueler to richen the mixture electronically, but still should be better than my carbed Sportster. May want to actually measure the A/F mixture and tracking. Then verify simple things like brakes not dragging, tires inflated slightly to the upper recommended range. Then do the mod to a custom or 5 gallon tank from a Dyna or Bagger...good luck with what you decide.:newsmile071: