I'm a huge advocate of 4 fletch.
Not only is it more economical when using full length feathers (2 great 4"er's as opposed to 1 great and one "second", if at all, 5"), but 4x4" actually gives more surface area than 3x5".
I originally went to 4 fletch to stabilize large surface area broadheads and stayed with them for their stabilizing effects on the arrow regardless of the type of head... including field points.
I can tell a difference in my accuracy when switching from 3 to 4 fletch arrows, don't find the extra drag affects trajectory noticably and can be assured that I've got the most stable arrow going.