Haha.
I see all these guys say 700-900 words for 5mins - mine was something like 580 words for this term...it's weird. Other guys wrote about 150 words more than me and did a speech of about 4:15. And the odd thing is that I couldn't really say it any faster (believe me, I tried)
So, there really is no estimate. Just type up 500 words, practice it, time it and then calculate approx. how many words are required for 5mins - that should give you a fairly accurate estimate.