120,000 is just overkill and wastes fuel. As long as your periapsis doesn't dip below that number your orbit will never degrade. I like orbiting at around 120,000 km just to be safe.
Even if an object in orbit is around 100,000 km in space it will still decrease in height by about 100 m each rotation until it starts entering a denser atmosphere, in which it will plummet much faster.
Originally posted by T.S.F.:Would just like to add my input.
