I'll be using 1600gph or so on my planted tank that's a 180 gal.

I can always reduce flow with a ball valve.

The wet/dry will run about 800gph.
Canister will run about 800gph.

Heater is in the sump, and the CO2.

UV in the canister loop and the Tee for back washing the filter/draining it, and for the tank drain.

Backing off the flow suddenly will always show pearling.
O2 can accumulate and diffusion is slower with less flow, does not imply that there is less/more growth however over time.

You would need a total O2 production curve over an entire day to see the differences.

But if you get good pearling and like the slower flow, and it gets the job done, then that's what I'd suggest sticking with.

That is what you want and you can see that, better than any test kit or ppm's reading. Flow can blow that off while still producing higher growth rates, thus you cannot tell as easily.

More growth is not always better, but I think a good visual cue it more important as long as algae and good over all tank health is good.

Regards,
Tom Barr