An interesting question came up which I'd like to also ask here.
Assuming you noticed something with your connection so wanted to go do a speed test, when is the most interesting or most efficient time if you will, to do that speed test?
Would it be when your latency changes a little or a lot? Say you know your average is between 20ms and 50ms for example so you want to pick a point that seems unreasonable like over 100ms or 300ms or 500ms for example. Again, this later decided upon by checking to get a reference point to start with.
Would it be if hops keep changing while you are watching them from the command line for example?
Obviously, both combined might be a good answer but are there some other things you might want to look for before doing that test?