>>I know the guys are renting it for a number of years, even before cloud became an IT buzzword. "Co-hosted" or something was the buzzword then.
>
>Maybe colocated? That would mean their own server(s), but on the premises of a 3rd party.

Never bothered to learn the difference :).

>If that's the case I'd expect your results to be more deterministic, unless you know it's busier with other stuff at certain times of the day.

I think that's the cause - the time of day matters a lot. Probably the number of users varies, and who knows what they may be doing, hence the variation.