Here's a new ocean test. I used two water shaders, but only for the main displacement, one for big displacement, and another one for small scale displacement. I then added a dark blue shader and another one with a brighter blueish color. Additionally there's a subtle twist and shear shader and some vertical displacement. The whitewater is created by using the Intersect underlying feature (favour rises). I have a reflective shader as well, but it's deactivated here for testing purposes.
In the original clip the white stuff is quite noisy, but after reducing the file size it became smoother. So, a loss of quality isn't always bad...
The good thing is, I can increase the size of the (internal TG-) plane, and the displacement doesn't change.