You don't have to manage SoT, it just happens and affects part of our damage while EP affects all of it. Then again If choosing MP makes you think more, instead of just mantain 6 cp rupture and dish out 6 cp envenoms (mostly) then we might have had very different experiences with the Assasination rogue.
Ok, you could start managing SoT with MP at higher mastery levels as if it were EP, due to the higher % increase to AP (I don't thing it would have to be much more, EP ~75% uptime against say ~10% permanent from fully stacked AP should be about it + -),