Regarding ~4%, I found better numbers.

If the combined mass of the planet and its trojans is between 0 and 2.85%, the system will be stable.

If the combined mass of the planet and its trojans is between 2.85% and 3%, the system will not be stable.

If the combined mass of the planet and its trojans is between 3.1% and 4% the system will be stable.

If the combined mass of the planet and its trojans is greater than 4% the system will be unstable.

This is from a discussion I had 8 years ago on the Cosmoquest forum.

http://cosmoquest.org/forum/showthread.php?58590-Orbit-of-Earth-changes