I use three 5" shield, they last a really long time for me. I shoot daily and I have some arrows that are a couple years old, maybe older. I have only been shooting traditional for a few years.
I think one reason that fletching last a long time has to do with tuning as much as anything. I will say that I do build up my rest, creating a channel for my feathers to have good clearance. Also using good feathers helps out, I have been mostly shooting wild turkey feathers that I have taken. The very worst thing for arrows is shooting more than one arrow at the target.