got a mail last week telling me my site was slow, with a screenshot form a comcast speed test site showing 460 down. that is a measurment of their line, not my server.
1- an isp test pulls one big file from a node that is probably in the same city
2- your site is lots of small files from far away, plus dns, tls and whatever js you shiped
3- the two numbers have almost nothing to say to each other
i sent back a webpagetest run from their own city instead and that endd the conversation.
Source: r/SiteOptimization · by /u/gvermeer