I lived in FL for a while as a young child (I was about 7). But I seem to recall that the lady that lived next door (she was a veterinarian), shot a 12 foot eastern diamondback rattler.
My mom seems to recall it being 12 feet long as well.
In some other thread here, in another forum, I wish to God I knew where, Rebel posted a photograph of what appears to be a rattlesnake--it's some huge snake with a diamond head--and so I can finally see where they could grow to be nine feet long (or longer), and as thick as a man's thigh.
I had never disputed "length;" I was always disputing "thickness," but again, Rebel's photograph resolved that issue.