It's more useful to know how the sites perform most of the time.
I'd also have been interested to know if tests were controlled for time of day. For example, the sites I host are almost all Australian and so the traffic I see follows a 12-hour wave as daylight crosses the continent from East to West, with small peaks around lunch time and after dinner.
What tends to happen is that spammers hit that file up and ask it to perform slow operations (the Wordpress team recently greatly expanded its capabilities). A PHP instance gets tied up for the duration. I've had instances lock up until killed by timeouts of 2 minutes.
When a bunch of traffic arrives at once, it only takes a handful of badly behaved instances of xmlrpc.php to render the server essentially inoperable.
I just went through this a few months ago. My bloggers don't use it and it can't be deactivated from within Wordpress any more, so I just 404 it in nginx.