Without knowing what microvertex jittering is... I'd say a new water seed could be the way to go, the water here has no specific so there will be no upset to change it although the only effect I can see happening from this is that it may just move the black to other places and waste domdib time (not something I am a fan of). Scales on the waves I dont think I have changed from default. Rough = 0.02, Wave = 10, Smallest = 0.1. Mostly i've just played with the colours on the sky.
Well, with increasingly long end tags this is what I have after postwork. Thanks to everyone for help. Now what else can be done?