I asked,
in regards to aliadiere's post below about Mo--not the length of beards in general.
Oops, sorry about that, I should have read the question correctly.
I just had another look - the only ones I've within the Sahih hadith collection found are regarding when he prayers that his beard was moving.
The one regarding one fist, there was no fixed length, so it plausible that it is as long as one of the previous posters said it was.
Although there is a narration where towards the end of his life that he had lost most of his hair and whiskers.