There are diagrams and clever schemes for dimensioning of pumps and filters. The pump capacity (as printed on its label is further reduced by the resistance of the pipes (diameter and length, number of elbows), check (return) valves, outlets jets, number of sucking intakes, resistance of the sand filter, height position of the pump. Different pressure conditions (and so the flow) are when inlet to the pump only from the pool bottom or only from the OF tank, or from skimmer(s).
For my 50,000 m3 pool I have bought my filter in GH (7,500B) and the pump (7,500B) at a (not pool) pump specialist (GH also have a similar pump). The pump label shows a range of 4 - 24 m3/h (with max H 16m), 1.1 kW (1.5HP), it gives me some 12 m3/h, roughly checking, I should better have the piping with a larger diameter.
I do not think that I would fare better when buying at a pool specialist for some 5fold price. The pump is running 4 - 6 hours every day, keeping the water clear without much chemical throughout the year. With a smaller pump the water exchange can be achieved by a prolonged filtering. The minimum and maximum of the necessary filtering time can be tested, whether a difference will be apparent.