I am playing around with anamorphic adapters, and obviously am limited by what sort of taking lenses I can use. I wanted to use a Zeiss 35mm but found it vignetted very slightly, so I moved up to a 50mm. This is on a GH4 with a Speedbooster, so fairly fairly close to simulating a Super35 sensor. Also shooting 4:3.
For Super 35, ~35mm-ish seems like a standard for a "normal" fov on spherical and 50mm seems a bit tight, better for close-ups (imo). But since the 2X anamorphic stretches the horizontal focal length, I am a little unsure of what should be a go-to focal length for anamorphic. I myself usually compose based on the vertical size of the frame, which doesn't change, but obviously I wouldn't want so much more negative horizontal space so I'd probably move backwards to compensate.
I don't have many other great primes that will take the anamorphic adapter, so I am trying to avoid too much trial and error by seeing what others think.