Interestingly you can see some of the trend between slow play and the best play when looking at that chart. In the fifth division down, the one with 913 players in it, the pros and master players are mostly grouped near the top. And just below that, where they have the divisions based on skill, Pro, Master, A, B, C, etc, you can again see the general trend where the slower the players the better the players.
This isn't enough on its own to draw definitive conclusions, but the totality of the evidence supporting that everybody (once you force yourself to get used to it and give it a fair chance) will play to their maximum potential when they play slow is overwhelming. The problem is that it just doesn't make for the best viewing experience and so there has to be some use of time clocks or similar that force a compromise between the best levels of play and the best viewing experience.