The great body of information on human expertise is driven by K. Anders Ericsson in Florida University, in the same way that relativistic physics was driven by Albert Einstein for a while. Ericsson isn't the only person researching this, but 100% of current research cites Ericsson or is done by researchers working in tandem with Ericsson. This is the peer review process: one researcher is developing all these findings, and other researchers are citing his work and attempting to reproduce similar findings with similar and dissimilar methods to explore, refine, confirm, or debunk.
Ericsson's large body of research effectively condenses to the simple principle of deliberate practice: that a person will develop expertise by practicing with technical goals in a manner providing constant and immediate feedback. Modern cognitive science defines practice as an activity which generates errors so as to allow the practitioner to learn to reduce those errors--for example, typing faster to the point of making typographical errors so that you learn to move your fingers more precisely and type faster without making such typographical errors. The researchers benefit from the hundreds of books and papers produced by these cognitive studies, but only the broad conclusions are useful to you and I.
In the paper like that I remember best, the thesis was that anybody could learn to be a great memorist, and the support was that one of a group of subjects had managed to do so.
Memory papers are interesting. Depending on how you measure the results, you get completely different outcomes. Do you measure the percent of things remembered, or forgotten? Do you measure the number of things remembered, or the number forgotten? Some studies show that random experimental groups memorize 60% of the information given to them, versus 70% for an untrained control group; yet, at the same time, the experimental group memorizes 48 of 80 items inspected in a long list, while the control group memorizes 42 / 60 items inspected in the list--the control group memorizes fewer items, and inspects fewer items. Do we base on time, or on number of items inspected? The control group may take 10 minutes to inspect 80 items, while the experimental group takes 6 minutes; if the control group memorizes more, do we attribute that to simply having more time, and can we assume that the experimental group would memorize the same number of items if they took 10 minutes?
Such challenges are inherent in all statistics-based science. As well, what you've described is a standard experiment: a group of subjects versus a control. Prescription drugs, for example, are backed by thesis that the drug will control depression or ADHD or blood pressure, with the support that a group of subjects has shown better mental health or lower blood pressure when provided with the drug.