Hey my friend. Well since you ain't got an answer yet, i'll hang out with ya for a while here. All i use is 'feather fletching.'
Started using it back in the 70's with recure bows, and 'still use it', cause 'for me,' it works great. I use 5" feathers that measure 1/2" wide at the nock end. To me they give 'more stability' than the shorter fletching.. this, of course, like ammunition, is up for debate i guess.
But i just never seemed to get the stability out of the shorter fletching. Keep in mind though, i do not know what you are shooting, that is what your 'set up is.'
I use recurve bows, they have ranged over the years from 70# @ 28" draw, (in my younger years), to 50, 55, and 60 #. These bows have been Bear, Martin, and one Herters, wish i still had the herters bow.
with the 60# i use easton xx75 2215's and 2216's. The 2216's 'for me,' have worked the best. All these have had a slight 'helical fletch,' at 5".
I used cedar for a while, in the begining, but switched to the easton's in the late 70's, because i had a hard time keeping arrows straight.
I suggest you look up "Three Rivers Archery" http://www.threeriversarchery.com/
They have some really good stuff, and perhaps may have some of the things you are looking for. They can sure give you the answers you seek i know.
with the above mentioned set up/s i have used, these arrows have all flown straight and true. Some people say feathers get wet when it rains and will not function properly, this has "never" been the case for me. I have never had a problem with that one at all.
Again, I do not know what you are using, compound, or recurve, weight , etc. etc. But, i do know that for my set ups, the 5" helicals have always preformed fantastic.
One of my brothers builds custom bows, (all long bows), folks have won tourneys with his bows, and he really does a very good job. Even with the long bows, the 5" fletch works real well. No problems at all.
As far as 'speed' some say they think they gain a little more with the 4" fletch, and this may be true, but even ole Fred Bear and some of the other old timers used the 5" fletch, and they seemed to have done ok.
I would gladly sacrifice a little speed, for greater arrow flight. Again, as you already know, this depends on your set up etc.
Well, i don't know that i helped ya much, but i had a few minutes here, and saw your post, saw i thought i'd holler at ya.
Good luck, and good shooting Hoss!