"We have shown that, even though the Internet induces significant timing jitter, we can reliably distinguish remote timing differences as low as 20µs. A LAN environment has lower timing jitter, allowing us to reliably distinguish remote timing differences as small as 100ns (possibly even smaller). These precise timing differences can be distinguished with only hundreds or possibly thousands of measurements."

http://www.cs.rice.edu/~dwallach/pub/crosby-timing2009.pdf

Inside Amazon datacenters you also have lan-like performance.