I have reported this before, but when I was at Luderitz in 2013, I was fasinated to watch while AA rigged, and re-riged his sail multiple time and tried 3 different masts. I was watching closely and I am slightly embarrased to say that I could not see what he was looking for, or, I mean I could not see the small differences he was seeing. As far as I could tell, all the masts were production masts and they all looked the same. He seemed to be satisfied he had found what he was looking for though.

Yes, even from the best factories, some of which individually test every mast to ensure it falls within their QC limits, there are slight differences between individual masts. Likewise, there are very slight differences between individual sails. These differences are usually very small and beyond the detection threshold of most of us. When you are as tuned into your rigs as the top professionals though, the differences can somethimes be detected and mast/sail combinations optimised for certain conditions.
At a more basic level, I am sure some of us have found a particular 'magic' combination of mast and sail that just seemed to work really well for us. I can think of a couple in my experience, (often PB rigs) and I have always kept those sails and masts as reference. But the interesting thing is that when I recently returned to have a test sail on one of my 'Magic' PB rigs from a few tears ago, I was surprised to find that it didn't feel any better at all from my current model equivalent, and the current model has noticably some better aspects. It's nice to confirm that we have made such progress.