FWIW the most durable rattle can paint job I have personally done was over the existing paint. I painted a frame and fork, but for whatever reason only stripped the frame to bare metal.

I roughed up the paint on the fork, exposing primer in most places. Sprayed a little primer over that and then color and clear. The frame chipped like crazy, had to be constantly touched up. The fork is still perfect, not a single chip after years of use.