What other kinds of circulation are you planning within the tank?
There is tank to sump turnover which is what you are referring to and there is flow within the display tank.
You will want some powerheads running also and that will add to the flow within the display tank. A system dominated with soft corals and LPS cannot handle what a SPS dominated system can.
There really is no specific rule of tank turnover, it mostly depends on what is in the system and the individual reefer. A system with a slower turnover will have a longer dwell time in the sump where there could be a skimmer and macro filled fuge. It also give longer dwell time in the tank for live rock biologicals to work.
You are also stating a GPH rate that is probably without any head pressure. If it is 850 max then at 4 feet it is probably about half. I think you are overpowered and would recommend not getting anything larger than the 500-600 max output with the addition of a couple nano powerheads or one larger one for flow within the tank.