No worries. You have shot WAY more animals than I have and with more general experience to boot!
The question was about 4 vs 5 inch feathers. That's mostly why I pulled my posts. I got your point and it doesn't really matter if African tribesmen shoot 4,000 grain arrows, 40 yards at game without fletching. I didn't really answer his question. I might have even been leading the average hunter, which includes me, down the wrong path. Tuning is very important, but the fletching can and will save you on a number of occasions.
The bottom line is; The arrow has to be flying true when it hits the animal for maximum penetration. Bigger fletching helps accomplish that goal.
Just as a side note... the African hunters did essentially bare shaft tune their hunting arrows! They cut them or added bigger heads until the arrow flew well. Interesting info from Ashby.
Now back to the original question; 4 inch will work fine if tuning is done well. 5 inch will be better overall if you had any issues while bare shaft tuning!
Good luck,
-Charlie