Goby, how are your pumps set up around the tank? Right now I'm contemplating a 40b build and I was looking at building a closed loop pushing about 800gph through an OM squirt on top of a 200gph flow through a refugium. Granted, the idea was SPS, but now that I see your work of art, I question those plans.
Have you ever checked your pH after lights out? No big swings?
I have them set in a Gyre type pattern. Starting from the back right the pumps are aimed in a counterclockwise rotation with the last one in sequence pointing against the flow to create some misdirection. It works well for my set-up.
Sounds like your plan is sound though. You could always drop the CL flow down from 800 with a smaller pump.