Sidewalls are your friend for a plusher ride off road. The P500 can use all the extra plushness you can give it. True 27’s fit and true 28’s start to give you some rub iirc from other posts.
You’ll also hear if you go up you need to go out with the P500. So if you aren’t width restricted put spacers on (or wheel offset) to help prevent tip overs regardless of tire rub need.