Does the weight recommendation on FCS fins still apply for SUP boards

I am near 90kg and looking at a thruster and quad set

But at my weight i think I'm better to go for PC7 and the equivalent in a quad set

PC7 would be a reasonable starting point. A decent all round fin.

Do they run the GXQ 80/20 trailers for the quad option ??

My preference is the big Merrick Fins, with a long base for drive. It suits the way I like to surf.

Kelly 5 sets looks interesting too, but expensive... But it is 5 fins, to cover all bases !!!

Are you mostly surfing beach breaks? The AM's are good for points.

Your original question was do the same recommendations apply for a SUP board from the general FCS guideline for size and weight.

The answer is NO.

The average tail on a shortboard is 13 1/2 to 14 1/2 inches. A SUP is more like 18 1/2 (mine is anyway) this means the back fin is much further away from the rail fin and with all of the additional surface area in the tail even with the same weight rider there is substantial additional pressure on the fin. A small fin like a standard thruster set up will slide with that much pressure or lack forwards projection.

As a Thruster I use GAM, MF or M7. On a SUP I use the MRTFX with the same size rear fin as a thruster set. They have similar drive IMO.