[OceanMan]

I am sorry to say that I think that not much thing can be said about the efficiency of the fins out of the test you did Dave.
Speed is irrelevant when judging the efficiency of a fin because you also need to know the amount of energy you spent to reach that speed which is, as you said, totally subjective here.

Maybe by using a good pulse oxymetre at the end of the dive... and doing enough dives to do statistics...

If I rely on my own experience, I would say that fiber is alway better than plastic if the stiffness is the same.