Longboard with QUAD SETUP

OK so this 8'2 Firewire submoon I'm waiting on to arrive is a 5 fin box so I can go quad or thruster....
I REALLY wanna try it as a quad just because it's going to feel so different. But does anyone recommend a fin size for it. I'm thinking large but on Future Fins website it states the large quad fins are for 198 lbs+ and I'm only 165 lbs. But the board is pretty much a longboard. Any thoughts on what I should buy? They're so expensive I wanna get it right the first time.
It'll be used in waste high surf mainly down here in TX.
I REALLY wanna try it as a quad just because it's going to feel so different. But does anyone recommend a fin size for it. I'm thinking large but on Future Fins website it states the large quad fins are for 198 lbs+ and I'm only 165 lbs. But the board is pretty much a longboard. Any thoughts on what I should buy? They're so expensive I wanna get it right the first time.
It'll be used in waste high surf mainly down here in TX.