If done well, you can't tell the difference between powder or paint. Powder that looks heavy, is, heavy.
As long as either method looks the part, it will be fine. It's usually the other details that really determine the value - chrome, bolts, gauges, paint etc.
I've always thought that the frame was somewhere between a gloss and a satin. It definitely has a gloss to it, but if you put it against a high gloss it looks satin. If you put it up against a true satin, it looks gloss. Who knew there were so many shades of black.
I do agree about the Rustoleum. It looks very close original.