Hmm, well, a quick search didn't find the one that I'm thinking of, but this one disproves the 5-6" limit.
XTube Videos
Of course, if you're REALLY up for something more extreme, in the related links, take a look at the user KirkJ, including the vid where he takes a horse dildo. No, really, I don't mean "horse" as in "big", I mean, it looks like an actual casting of a real horse's dong, and almost as thick as the skinny guy's LEG, and appears to go deep enough bump into his shoulder blades from the inside.
It's NOT for the easily disturbed.