I started riding the 6-4 HELLFIRE FST as a trifin using others suggestions to use the largest fin possible as the board is already set up to be loose and you want to stiffin it up.
AM-2s (TRIfin) (4.79 fronts with 4.5 rears) worked great. tested on 1.5X overhead waves. Drove As hard off the bottom I could lean into without my knees catching the wave and they held great. Cranking off the top/lips the fins held nicely power turning as tight as my body could contort in comfort zone. Pumping down the line easily captured the speed I wanted for each manuver ahead. I knew if I had better knees I would be attempting airborn missions no problem with that speed. I cant wait for a decent backside day soon to test my heavy back hand carve displacing bathtubs of water.
Stamps (QUADfin) 4.54 fronts with 4.0 rears) tested at Head high + waves. These fins worked best on a point break and absolutly flew down the line on any pump, sometimes a little too fast for me to read the wave ahead. I feel the back fins might be a little large for the waves that day as I was not getting the release I wanted out of them.
Next test...Stamps fronts 4.54 maybe switch the Stamps 4.0 rears out with the Rusty 3.85 rears. On a bigger day I might Pair these Stamps rears 4.0 with the AM-2 fronts 4.79.