depends what you want je can make pistons up to a 108mm. i wouldnt reccomend going that high without sleeving however. due to getting into the waterjackets, which results in water in oil and a million other problems.
my reccomendation would be a stock bore high comp piston, JE Can make you anything you want with a min order of two pistons.
Im personally planning to put a 11.5 comp piston under the seat of mine. most big bore kits only raise the comp to 10.1. so 11.5 or 12.5 with a stock bore could be a good solution for mudders. as it will give more low end/torque and a more responsive engine. whilst maintaining the engines reliblity for the most part.... a moderate compression increase shouldnt effect wear that much. just make sure to run the right octane fuel, and to stay with 12 or below. its not a can am and wont do well with a 14.1 or a 15.1 piston