Values higher than 100% are possible, but do not provide any additional benefit. NPCs will only interact with you if they are scripted to by a current quest or if a guard is attempting to arrest you. It is possible to combine multiple Chameleon enchantments to reach 100% Chameleon, causing your character to be visually non-existent and nearly completely undetectable while performing any actions.
Oblivion's Chameleon at 100% (emphasis mine): It appears to work similarly, though at a lower percentage.