Here's my thinking. At some point, you would have enough flow such that the concentration of stuff in the water in the sump would be the same as the concentration of stuff in the water in the display, call it "well mixed", in which case, it wouldn't make a difference if you had the skimmer in the tank instead of in the sump, or if you had no sump ("well mixed" in the DT being achieved by powerheads, well mixed between the sump versus DT due to high enough turnover).
Once the water in the system could be considered "well mixed" I wouldn't think increasing the flow to the sump would matter. At that point, the driver would be what flow is required by all the things you want to do with the water in the sump. As long as you have enough flow for that, then adding more wouldn't help, and would just cost you energy for moving that water through the system.
Once the water in the system could be considered "well mixed" I wouldn't think increasing the flow to the sump would matter. At that point, the driver would be what flow is required by all the things you want to do with the water in the sump. As long as you have enough flow for that, then adding more wouldn't help, and would just cost you energy for moving that water through the system.
