It depends on how you see it
From my point of view, if there is too much water flow in the sump, it only acts as an increase in the total volume of water.
Different people have different views so i think that research is VERY important to ensure you are using the sump at 100% effieciency.
As for fuges, I am currently trying out a new design where there is high flowrate on 1 half and low flowrate on the other and each half will have Grade 0 and Grade 1 sand respectively.
Any details of the head loss from output of chiller to return to main? i do not want to have too many pumps working