Personnaly, if going off road, i would keep a short cage derailleur. I tried medium and the bottom pulley kept getting caught. With shimano current short cage (equivalent to 10yrs old medium cage), i run 36T without problem and 40T with the better derailleur.
if you are just using the bike on the road, medium is “ok” although in the British winter it is not great as the pulley get covered with mud, salts etc