The difference will be slight if any. Your FOC will increase slightly but not enough to make a difference in you arrow flight. At close range out to about 20 yds you will pick-up some speed. Afer twenty yds. that will revese itself with drag. Feathers are more forgiving and will stablize your broad head better. As far as 4 or 5in. helical. I think that will depend on your rest or launchers or if you think 5in. will help stablize your arrow better. I shoot 4in feathers and get great arrow flight w/carbon selects and muzzy's. Rain and snow will effect feathers. Even if you water proof them they will not with stand a long down pour. That is somehting to consider. Hope this helped. Jerry