Maximum Amplitude of a Lissajous Orbiting Object in a L4 or L5 Position
Is there a ceiling for stable L4 or L5 masses?

Your link says orbits about Lagrangian points L4 and L5 are dynamically stable  so long as the ratio of the masses of the two main objects is greater than about 25. 

Earth &lt; 4% Sun = Stable L4,L5 points

http://en.wikipedia.org/wiki/Giant_impact_hypothesis says that the Lagrangian object would destabilize once above 10% of the Earth's mass.

L4 or L5 object &lt; 10% Earth = Stable object