Id imagine its pretty low for limit since bad players tend to play much more correctly. This is partly because there are fewer decisions to make (i.e. no bet sizing) and also because a fishes natural tendancies (i.e. call too much) line up alot nicer with correct play in limit than they do in no limit since the pot odds are so much bigger. If the worst players play almost correctly then your edge is going to be very small.

Id imagine its pretty impossible to make a mathematical proof of your maximum winrate since it is still a function of how bad the competition is.