We use iperf for performance testing: when commissioning circuits we create a private network and protect the rest of the traffic from it to ensure consistent and meaningful results.
We have bulk transfer tests, and sweep-ping tests during bulk transfers. telco sometimes fail to deliver the committed bandwidth on the first try, or extraordinary levels of packet loss under load. "Trust, but verify".
I find speedtest a fairly pointless test for a random user (if you aren't getting close to 99% of your uplink speed as the download from their server then the problem is either their server or too many people testing, or both.)
