A few years ago, an archer here wanted to get away from 'hunting arrows that look like target arrows'. He had me fletch up some heavier arrows for him, but he wanted to know how much speed they lost at 30 yards and he was concerned with how much penetration he would lose or gain. He practiced and practiced with both arrows using a bow sight. He got a hold of chronograph. Up close they the heavier larger fletched arrow was a little slower, but the math went in favor of the heavier arrows. He then backed up to his mark and proved with the first shot that he had enough penetration. He put the first arrow right through the heart of his chronograph and killed it dead.
As far as killing efficiencies of flu flu arrows. When I used uncut four fletch the arrow cast was not all that much different than 5.5" three fletch, but the arrows came down straighter when shooting at pheasants and easier,(sometimes), to find back. With the double wind style, they slowed down a lot, to a point that I could not use steel blunts on pheasants and the shots that I was getting at pheasants tended to be outside of a practical and predictable range of the arrow flight with wind also being a negative contributing factor. I prefer to use normal fletched wood arrows that have seen their better day or the cheapest crap shafts that still fly good. One that always impresses me is when I break a point off of a broad head length arrow and replace it with a blunt, I get a net length arrow out of the deal. One would think that would make an arrow that was way too stiff. Too my surprise with a Hill style longbow those shortened net length arrows fly very nice and are more predictable than any flu flu.