if you get tons of methionine and no cysteine, your body will donate the sulfur from methionine to form cysteine, but that's only one aspect of conversion (called transsulfuration) and while it may be limiting it seems to be wrong to erect any enhanced importance to the connection. conversely, if you get tons of cysteine and no methionine, your body will rebuild methionine from homocysteine, but that has little to do with your cysteine intake, besides the sulfur component as the limiting factor. the amount of methionine that is actually needed is minimal.
so, these numbers that they give you of total sulfur amino acids are in truth of minimal value in determining what you need to maintain optimum health - you are going to need more of both, clearly. it's just about how much sulfur you need, under the assumption of ready conversion.
what i needed to know was how much of each that i needed to get to stop them from converting into each other, which is almost the opposite question that people want to ask (which is how much cysteine you need to minimize methionine requirements). so, how much cysteine do you need to stop your body from converting methionine to cysteine? that 10.9 number was presented, but i'm not following the argument, and wouldn't advise citing it. i erected a very simple linear approximation, but i want a more direct measurement.
let's hope i'm awake and clear and focused enough to figure that out before the sun comes up.