Zimmanski
Aquarium Advice Addict
I don't know about that... There is a Clown Knife in a LFS just down the highway from me that I could probably cram into a 40b with some grease and a plunger (not that I would). The thing is just HUGE.
I've seen a monster clown knife too, like the one you're talking about almost, but I would probably lean more towards the 20" on average for most people.