In principle, speed fins are extremely fast and small slalom fins. They have to offer top speed and top controllability. Their profile is extremely flat and thin, and should be of the laminar type. Lift force nearly does not count, just speed.
There is still an ongoing discussion concerning the rake angle. Some producers are offering speed fin with about 30°, while others prefer around 15°. Personally I would rather stick to the latter.
For speed records you need a smooth water surface which you mostly find in extremely shallow water regions close to land. Therefore, fin size has to be reduced to a minimum. For these conditions speed fins are designed with a very wide base and an outline close to a triangle to minimize draft.