I use 3" " Kurly vanes" simply because thats as big as they make that vane.
I can get Muzzy heads to fly perfectly, and group right with my field points. Going to Slick Tricks makes it even easier!!!
I went to the Kurly vanes to get some more FOC (they weight LESS than feathers!!!). Now that I am going to 125gn heads, I MIGHT go back to standard vanes (PROBABLY 4" MAYBE 3" we' ll see).
BTW those light vanes sure made for a quick arrow (300 fps) and as a bonus, this is a place where it' s almost a free lunch. More speed, and STILL great accuracy AND penetration!
While on paper the heavier arrow might have a touch more KE...some of that KE is in the feathers/vanes. feathers/vanes do NOT transmit KE as well as the shaft and/or broadhead does