On a well tuned arrow it doesn't really matter.I did a few years ago on a dozen arrows,I fletched 3 with 3-4",4-",3-5" and 4-5" feathers.They all fly great and grouped together at 20 yds.They may not have the same trajectory when shooting 30 and 40 yds,but at hunting distances made no difference.I used to shoot larger feathers when I shot wood arrows like 3-5.5" and 5.5" banana feathers but my favorite has become 4-4" parabolic and shield with all my newly fletched arrows.I have tuned arrows with 2" Blazer vanes for an ILF.I feel tuning an arrow is more important then the size or number of feathers you choose.