The main reason to shoot 5" is if you happen to like them. 4" will work fine. Last year was my first time hunting with 3" feathers. They worked great. Broadhead and fieldpoint impacted right next to each other. This year, I'm thinking about 3" vanes. Your 4" fletchings will work great. Like anything else, make sure you tune for good arrow flight. Above all, archery should bring you joy; use whatever fletching size makes you happy.