RE: 4 inch versus 5 inch fletching
IMO both 4"and 5" are overkill no matter what the arrow length
if you shoot a wisker biscuit with a bow that has a 7" brace heighth you will find that even a 4" fletch will bury up into the wiskers at rest
if you are using enough helical a 3' feather or vane will work good but I recomend the Bohnning Blazers for more down range speed and a more stable flying arrow farther out, ie the more down range speed the arrow maintains = maintained arrow RPM down range wiich also= better broadhead stability down range.