Brian, I am not sure what "automatic ltd.slip" is, (they all work automatically when needed), maybe someone with more knowledge about the modern cars will chime in here.
40% LSD is what the factory puts in diff and is what you want on the street. Every differential, (except maybe drag cars), must have a certain amount of "slip", ie. allows one rear wheel to travel at different speed than the other, otherwise rear tires would be scrubbing and fighting each other every time you turn. If a car does not have ltd.slip, (one wheel wonder), and only one wheel spins on ice while other one stands still, that would be 100% slip. (One side is getting 100% of torque, other 0%). A 40% LSD means that maximum "slip" is 40%, left/right.(Or vice/versa). Hope that helps. It is definitely a desirable option on your car, w/ HP it has.
