Google's page loading times seem kind of flaky. One of our sites' loading times has jumped between 1.5 and 10 seconds and back four times since they started graphing it.

But I have a cron job that tracks the loading times of random pages on our sites (from offsite, every 10 minutes). I get very consistent loading times (nowhere near that variance).

(Edit: they also suggest GZIP resources that are in fact already gzipped, at least they are according to the HTTP headers)