It'll be more realistic then DC -> DC queries.
- http://www.w3.org/TR/resource-timing/
- http://googledevelopers.blogspot.se/2013/12/measuring-networ...
That depends on what you're trying to measure. If you want to know what the total end-user experience is like, Resource Timing is awesome.
If you're trying to compare DNS providers without noise from the differences in client implementations and ISP competency, however, it'll be very noisy and you need a massive number of samples to avoid seeing trends which are really just sampling artifacts.
The best approach would be to do both so you could compare the server response times with the measured client values so you can get an idea whether a slow-down this week is caused by something you have any control over.