I wasn't satisfied just comparing pitches over 100mph to pitches between 90-92, so I broke things down into something of a continuum. The results:
Once you get into the upper 90s and triple-digit range, you start dealing with sample size concerns, along with concerns over the matter that there are only a few guys who can throw that hard, potentially biasing the numbers. But what's abundantly clear - and what comes as little surprise - is that the harder a guy throws, the harder it is to square him up.
It's interesting to note the contact drop between 96-98 and 98-100, since we're still dealing with samples in the thousands.