Auto Smooth option and Edge Split modifier give essentially the same result starting from Blender 2.71 when the support for the sharp edges and split normals preview in the viewport was added for the Auto Smooth.
There is one difference though - Auto Smooth doesn't actually split vertices, it only shows them as split ones. Hence the result of the Auto Smooth is visible in Edit mode but is not editable (e.g. to move out the faces which fell under the angle threshold).
To preview the split normals in Edit mode uncheck the Auto Smooth and add Edge Split modifier, then apply it (depending on the case it has to be in the bottom of the stack so it doesn't interfere with other modifiers and has to be applied last).
It is still possible to undo the results made with the modifier by removing doubles in Edit mode.