In the "Tiny Tina's Assualt on Dragon Keep" DLC for the game, you can find a weapon called the "SWORDSPLOSION!!!!". One of the features of the weapon is a ~500% melee damage increase. Playing a Psycho in the game, it seems like that weapon should be insanely good. However, it doesn't appear to magnify the actual melee damage of the Psycho. The (now massively underpowered, but for the +200% melee damage) "Rapier" from the Captain Scarlett and her Pirate's Booty DLC has been my staple weapon as a melee focused Psycho. I can't tell what the +500% damage applies to for this "SWORDSPLOSION!!!!".