Neil is somewhat correct regarding automotive filters, not much info on pressure drop vs. flow but on industrial filters , such as the Pall HH7400 filter that Buddy is planning to use you can find extensive information on pressure drop vs. flow rate and how it is affected by such things as oil specific gravity. Yes, having a filter between the high pressure pump and the engine does protect the engine and is the recommended setup by many dry sump pump manufactures, in the industrial and aerospace hydraulic world, were we are talking about real pumps at high pressures with exotic fluids, the preferred position for the finest filter is in the line that is returning oil to the system reservoir, the scavenger sections in our case, because this is were all of the crud from the system (engine) is returned to the reservoir. Why have this junk be pumped by the most important section of the scavenger pump package, the engine pressure pump, before it is filtered into the engine. Every time a piece of contamination runs through the high pressure pump and causes damage it makes literally hundreds of additional contamination particles that accelerate wear of both the pump and the engine. Doesn't make much sense to me no matter what the scavenger pump manufactures say.
Rex