Beyond the basic parameters of cracking effort, IP, and in some cases a service-tech adjusted venturi assist, regulator performance is by and large a 'feeling.' This is why all the ansi testing results give such a poor picture of how regulators actually perform in use, by divers. It's also the reason that different divers can have such different preferences about what they think of as "best."
I would not underestimate the sensitivity or perception of an experienced human to very slight differences in pressure and the behavior of air in his breathing canal. Evaluating a regulator performance on a high level is a little like wine tasting; somewhat subjective within established norms.
Most of the subtle differences in the way regulators perform are based on design characteristics and/or materials, not just technician adjustment. But a good tech will definitely know when things are 'right' and not just set within the range provided by the manufacturer.