On average on my 07 UC with big bore, SE 255 cams ,V&H TDs with ovals & fuel pack gets about 40 and depending on wind it drops a lot.Seems like MPG gets better after some modifications to the motor, friend of mine has 04 UC and his MPG improved a lot after bumping up to 95" with cams.
When I was stock I averaged 41. After the mods I am consistently hitting 38. I am not disappointed as the bike runs great! I run the highest octane as possible-usually 93.
Average is 38-40. Stage 1 with PCIII, K&N and an SE AC set up. I ride pretty easy but keep the revs between 2500 and 3200. No dyno tune - I can imagine the mileage would get worse with a dyno, but maybe not - can't afford one so I don't know. Mileage was
better stock, but the motor ran way too hot so the trade off was not worth it.