Here's a curve ball. I have been shooting 5-5.5" 3 fletch for over 50 years. With the cost of feathers nowadays I tried four fletching some of my arrows so that I could get two 4" fletches from one feather. I think my Jo Jan indexer is 75x105. The new four fletch seems to shoot flatter and so far my bhs seem to group better. The arrows seem to straighten out quicker, as well. I did some of my wife's the same way and now all her hunting arrows are four fletched with 4" feathers. Howevr, in response to your actual question, you should be fine with "just" 5" fletch.