3 fins will give you more speed through the flat spots but for tighter turns on a mush wave you will definitely want a twin fin set-up or a quad. If a quad, absolutely have much smaller trailing fins. Experiment if the crowds, conditions and time allow you to.
In punchy waves, you might not feel the difference...but in mushier waves, my experience is that quads glide better than tri fins. Both quads and 3 fins can turn on a dime, but 3 fins are much more forgiving on foot placement through turns.
Lol. As I break away from my thruster up bringing, I have found that there is much to learn... Evolving with these different set ups. LB has certainly provided some solid info lately! LB, your point about quad fin placement...16", is that width at leading edge of fins?
Tail width measured at 12" up from the end of the tail. Nose width is measured the same way. This is the "Rusty" setup... about 2" in from the rail for the rears; about an 1 1/4 for fronts, as measured at the trailing edges of the fins.
So, for hpsb quads you will have less spacing (distance from rail) versus wider tails... What is typical tail width for you on a more performance shape?