On average and at sea level a Stock EFI 883 will get "about" 60-65mpg, a 1200 will do "about" 50-55mpg.
A stock EFI TC88 in a FXD or lite FXS will do 45-50mpg, a TC96 will get "about" 40-45mpg.
A stock EFI, FLH or Dresser FXS TC88 45-50mpg, a TC96 35-45mpg.
These are just averages from personal experience from stock bikes in good tune.
Millage has A LOT TO DO WITH THE WAY YOU RIDE and the TUNE of your bike.
I can get 40mpg from my 103 BBB or less then 20mpg if I put the spurs to her, same gas same rider and road.