Yeah that's what I'm concerned about. I would be dropping from medium to small sized fins, something I haven't messed with especially in bigger surf. Would that be pushing the size small fins to much?
sometimes the small, medium, or large is included in the design and not so much the actual size of the fin.
Look at FCS's simon anderson fins. Area wise, they are a small, but listed as a medium. they seem set further back in the tabs with more rake and so on.
which fin system is it you are using? the difference doesn't have to be so drastic.
the accelerator mediums are identical to the old G6 template, which was between a G5 or m5 and m7 in size.
The accelerator smalls are closer to medium fins and I use these in my step-up instead of a generic set like the performer smalls and so forth.
some other in-between medium and small fins would be the old YU's and the mid size AM sets