look up specs for oil pump max pressure at its rpm. Take each gear to that as a minimum..
most often it matches torque rpm, but inlines are extremely offset, you need to look in the book mechanics usually have...
especially inlines, they need that max squirt between the gears. It will never ever be a low rpm "torquer" matching all parts together. the boxers for example..2850 is max torque and oil pump and progressive secondary...all at the same magical rpm..
If not to know or find out, at least 2800 rpm, and again, the inlines could be a universe apart within itself.