thanks for your information. I also asked Subal and they are recommending the 14-24 over the 16-35 for this kind of setup (D810/850 and 230 dome), unless shot wide open. But stopped down to f/8 - /f11 the 14-24 performs better. They also confirmed (for Subal housings) a different length of ext rings for both lenses (90mm for 16-35 and 65mm for 14-24).
I probably will just try it for myself. I can use the 14-24 for land shooting should it not perform under water.
Somebody else having first-hand experiences with the 14-24?