Average speaker is 150, an auctioneer is 250-400, the fastest person. The fastest talkers male and female can recite over 500,600 words per minute.
People can certainly and some people while exited/upset may.
Someone speaking a language like Chinese, where most of the words are single syllables, could probably speak a lot faster than someone speaking, say, German, where the words are often super long.
That's just my mostly uneducated guess, though. It'd be interesting to see some real-world comparisons of this.
I realise 500/600 looks like 5/6, but 500,600 reads to me as 500600. Maybe | is a good unambiguous character to use for "or".
As Y_Y already indicated:
> I realise 500/600 looks like 5/6 ….
If we're going to fuss about typography, these things:
> 500-600 wpm; 35-75 Kph; 2-3 grams.
are hyphens, and you want an en-dash: 500–600 wpm instead of 500-600 wpm.