For me it depends on the conditions. Our downwinds are often with wind-generated chop ie short and steep.
I tried the Fenn elliptical rudder which is smaller and thinner than the Orka rudder. For me, the Fenn didn't work so well; in such conditions I prefer the bigger Orka rudder.
But on the flat, or on big ocean rollers, I can imagine that the thinner Fenn rudder might offer less drag.
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...