13,800 feet.
An article in The American Spectator quoted a secret CIA report that Flight 800 was at the very extreme limits of a shoulder-fired SAM, and it would have been a very lucky shot. The warhead on a missile like that is very tiny, and is intended to destroy the back end of a jet engine, and not vaporize the whole aircraft.
Also, high-bypass turbofans mix lots of cold air with the exhaust plume, making for a much less intense IR source for a heat seeker. Modern turbofans on airliners have a form of "built-in" IR protection.
But a couple of pound of Semtex, placed on the floor in the right seat row inside the plane, will decapitate it. The 747 is built in pieces, and then joined together. One joint is where the nose/first class section joins the more tubular main part of the body. Aerodynamic forces would instantly finish the job started by the explosion.
We know the crew had no warning of what was happening. Get hit by a SAM, and you at least have enough time to get out a mayday, even if you don't know what's causing all the red lights to appear. But they were flying along fat, dumb, and happy, then the entire front of the plane was sliced off. Even a large SAM can't do that, but properly placed explosives can.
I remember that Algore was talking billions for airport security, paid for by the airlines. Then all of a sudden "center fuel tank explosion" became the official answer, and millions of dollars from the airlines appeared in the DNC bank account.