What size quad fins to make?

I am building my first board with the wonderful help of sways. Board is a speed egg type shape with slightly pulled nose and tail (rounded pin).

I have been trying to make it for super cheap and the fins plus boxes are suddenly are going to more than the entire board so I am going to make some and glass them on.

Board is going to be a quad and fins made from birch ply with a couple of layers of glass over the top. Board is 6’10 x 22 1/2" x 2 3/4. Plenty of volume as I am 6’5 and 220lbs low rocker and full rails.

This board is meant for use in good very fast waves. Down the line speed and hold is important, turning is not. Trimming and gentle carves are about the height of it.

I’m going to go for more rail fin approach then the mckee setup.

How big should I make the fins? Any other giant quad riders out there? Thank you so much.

Hope your paddys day hangovers are better than mine…

5"x5" fronts , 4"x4" rears, spaced about 1.5" apart and 1.25" off the rails. Single foiled rears for the big guys. Use a screen grab of the Future WTC or the FCS Kelly Slater 2.1 fin (same thing) and resize it to those dimensions.