Here are how I understand the zones (in a very simplistic form):
So I looked at the swinging strikes, run scoring plays, hits, and out plays on the 95 MPH + fastballs and looked at things like release point, location, and count to see if there was a common thread for which ones were successful, and which ones were not. Also, for comparison, I looked at every fastball thrown at exactly 91 MPH so far this year, what you might call league average, and looked to see if there was a common thread for successful average fastballs (you may have to click on it to get a full view of the chart)
Not surprisingly, the 95 MPH + fastballs got more whiffs, and more of the 91 MPH fastballs were put in play. The same percentage of all pitches went for hits, which means that the 91 MPH fastballs have a lower BABIP. I can't really explain why this is the case, as the 91 MPH fastballs have a higher amount of run scoring plays, suggesting that they are being hit harder. This may just be randomness or small sample size. Oddly, the release points of the 91 MPH fastballs are higher than the ones of the 95 MPH + fastballs, and while the lefties are more out, the righties are closer to their body with their release points.
When looking at the plus fastballs, the vertical release point is the same for all results. For righties, there appear to be very little difference in horizontal release point, though the closest to the center of the rubber for lefties gets whiffs or outs.
Not surprisingly, even when looking at plus fastballs, the slightly faster fastballs on average are more likely to get whiffs. There is no real velocity difference between the ones that are turned into runs, outs, or hits. The zones suggest that the runs are higher than the rest of the pitches, though there isn't much of a difference between the whiffs and outs/no out pitches. Count, especially when it comes to balls, may be the best indicator, as the less amount of balls the better.
With the average fastballs, height was a bit of an indicator, with higher being preferable somewhat (though outs being better than whiffs and runs better than no out plays hurts the case). The zones broke down much differently than we saw the plus fastballs break down. The higher the number the better it seemed, meaning low or out of the zone got whiffs, while up in the zone gave up runs. It isn't surprising that location is more important for average fastballs than plus fastballs. Horizontal release points, whether left or right, really provided no help with the average fastballs. Count wasn't as helpful as an indicator as it was for plus fastballs as well.
One thing this obviously doesn't take into account is hitters faced. We didn't look at platoons, and we didn't look at quality of hitter. By definition, better hitters will provide worse results for the pitchers on average. With that said, we didn't really see anything we didn't expect, though I thought release point would play a bigger role than it did. Getting ahead in the count early is very important for elite fastball pitchers, to just to keep hitters off balance and make sure they aren't sitting on the fastball. For average fastballs, location really provided the difference.