When you're dealing with a machine that is exchanging air in a room a certain number of times per hour and a continuous influx of particulates, with less efficient filters you need more air exchanges which means more filters, bigger fans, etc.

The takeaway is that less particle efficient filters won't ever get you down to the same steady state as better filters in real world applications.

And from personal experience with filters and devices to measure airborne particles, it is hard enough getting good numbers with the best filters I can find.