如何衡量网站托管的地理访问时间？

I'm building a website targeted for US visitors; and this question came up while shopping around for reliable web hosting there. Since I'm located in the UK, a simple "ping" wouldn't represent the average access time from a US visitor's point of view -which is critical, since a new visitor spends around 3 seconds to evaluate a website.I'm building a website targeted for US visitors