I'm pretty sure Wolfgang will respond here.
My guess is that you would be better on your 8.0 m2 rig with a 36 cm Duo Cut or Formula Duo.
If you plan to get larger rigs (than 8.0 m2) then perhaps the 40 cm Formula Duo would be better still.
I have the 32 cm Duo, the 36 cm Duo and the 40 cm Formula Duo and use them all the time. They are really my favorite fins for any kind of weed or shallow water conditions.
Hope this helps,