Andy:
I have been shooting 4 fletch for more than 25 years. I shifted to four fletch because I like the idea of being able to nock an arrow without looking. I quickly found out that I got better arrow flight, no doubt due to the greater feather surface area.
Over the years I have evolved to 4-4" fletch and now shoot 4-3" fletch with 650 grain arrows and 300 grain broadheads.
I have done a bit of experimenting at the indoor range looking at arrow velocity and grouping with the following combinations: 1) 3-5" fletch, 2) 4-5" fletch, 3) 4-4" fletch, 4-3" fletch, and the 4-4" fletching spaced at 90 degrees, and at 75-105 degrees. These tests have been with Arrow Dynamics tapered carbon arrowsand with two bows: 66# Big Horn recurve, 55# Dalaa recurve.
The results-I can see no differences in velocity (except perhaps a small increase, ~1fps, using 4-3" fletch), and no differences in group consistency. Hence, I have gone to 4-3" because I believe that I may get less arrow noise.