Do the word pad, clicking for a bit.
Get an idea of where your "average" click speed is.

Then periodically tune yourself at the target dummy.
Observe that each spell is casting, basically as soon as the dot expires or the spell refreshes.
Check also, if its a dot, that you are letting it expire before you recast it.

Even if I am a steady clicker at 2 clicks per second.
That doesn't mean, over time I won't become a steady 3 clicks per second person.
Tweaking the clicks/commas every now and then is a good idea.