I'm not sure this is a metric a web developer should care about. I always assumed the website would deliver the same X bytes of data, at the same level of performance for each request, regardless of source location. If this, or any other test says your site is slow from a particular location on the net, what can you possibly do about it? You aren't really measuring your web site performance you are measuring the quality of the pipe in between the two sites, something you have no control over.