Have you considered the Matrix Edge fins?
20 Fathoms - Matrix Fins
They have an angled blade and side rails. The rails aren't as tall as C4 rails though so that you can still scull. They come in 5 different stiffnesses.
I have used the Edge's predecessor - the standard Matrix - in stiffness #3.
When compared to the C4 blade, the Matrix will be wider, and they can be put in various footpockets - Sporasub, Omer, Picasso.
Very durable and reliable - never had to worry about them breaking of getting damaged unlike my C4 flap 25's.
