My Experience...I shoot both 3 fletch 5 in on my 55#bow...But 4-3in fletch on my 42# bow...
The only downfall is with skinny shafts, helical isn't fun. The shorter feathers are easier to put helical on skinny arrows...
4x3=12 in steering
3x4=12 in steering
------------------- the real dividing line
4x4=16 in steering
3x5=15 in steering
--------------------
4x5=20 in steering I think this is only needed if
the arrow isn't tuned well...
It is easier to just grab and go with 4x, but to be honest, it has never really ever made a difference to me....