RE: Apollo Vs F161
Per my other post on the iSonic thread, I use a 51 cm True Ames Shallow Water Weed fin on my F-Type 148 (now iSonic 155), with a 9.5, my largest sail at this time. It is supposed to have as much lift as a 65-70 cm Formula fin. It has been working well for me with the 9.5.
I would bet it would be not as good as the 75 cm formula-style fin on the Apollo, but that it still would be okay.
I have tried both the 43 cm True Ames Blade Weed and the Gsport 42 cm DC-Driver fins with F-Type 158 and 148. Both spin out like crazy, especially with a 9.5. So if you can live with a 51 cm shallow water weed fin it would probably work okay for the Apollo and great for the iSonic 155.
(I go down to the 44 cm Shallow Water Weed for 8.5 and below...)