They're quite closely related.. I'm unsure of the morphological differences that separate them, but temperament wise, it really depends on the individual snake, and species.

I've personally found kings to be more aggressive. I have 4 cali kings.. only one I pick up without gloves. I also have a speckled king who would just love to eat my fingers. By far my most docile king is my greyband. I love that snake.

As for milks.. I have three hondurans. None have bitten recently.. the only one who ever did is my baby het hypo. She doesn't do it anymore.. she's calmed a bit with age. All three like to wiggle around a lot though.

My albino nelson's milk is a very docile little fella. Never bit.

That probably just confused you more than anything.. oh well.