Take both and change them out every once in a while, you will be riding all day and the change will be welcome. I do not recommend this to others as it might could reduce the protection of the lid but. I also have an odd shaped head I have gone inside the helmet and shaved off just a bit of styrofoam where it is pressing against my head too much. Wearing an altered helmet is better than a half or even none at all which I do sometimes. Good luck on the iron butt, did it a couple of years ago, left early in the morn and back that night. Plan your route with the least amount of turns and make a plan for your gas stops. Those receipts are needed for turns. Also remember to hydrate, the wind sucks the water out of you.