I have gotten as high as 52-53 on several tanks of high altitude low speed cruising and anywhere from 36 high speed interstate to 48 moderate speeds Average in the low-mid 40's. Rinehart slip ons big sucker and stage 1 tune, almost always two up.
41-43mpg seems about normal for me 09 Road King bone stock, no highways here just a lot of putting around. I think the first 1k miles a got a little less than what I get now. My lowest I think has been 37 mpg and highest 45 mpg.
i average around 48 on my tc88 with minimal performace parts (stage 1). also i ride like im trying to keep this bike awhile, not trying to destroy it. Your aftermarket parts will effect your horsepower which will directly effect your milage.