I am on a big efficiency kick these days. Since you already have the pumps, you have to weigh the loss of replacing them and the cost of new pumps against the energy savings. If its several hundred dollars to get new pumps, how long will it take to recover that in energy saings? Just another thought.
If I was starting from scratch, I would use a smaller return pump simply because a large one is not necessary. Most of the necessary flow will comes from the CL. I also feel it allows the water to be processed a bit better by your skimmer, fuge or whatever. Also less worries about microbubbles getting back into the tank.
As for reducing flow at night, I think thats a personal choice. If you have lots of rock and good hiding places, the sleeping fish wont be bothered by the extra flow. Reducing flow may allow night feeding polys to extend further though, but thats just speculation. Wouldnt be hard to run a couple of Darts, one on that OM 4-way and one for static flow. Then you also have back up in one goes down for maintenance, you will still have some flow.
Did that make sense? hahaha..Too many choices...
