NOone in the AC biz uses how much drop you get as a parameter in judging AC performance. Not how GM, or BMW taught me, where did this method come from?
It is not part of the ASE cert. test I took and passed, or the refridgerant handling class or the Community College class, or the GM FSM.
And your perception of how good a job is done has the humidity of the air around you as one of its parameters.