This poll and http://www.cointalk.com/threads/guess-the-grade-546.234175/ will be closing tonight. Break time probably until the 28th, but the 24th is unlikely, but possible.
Most all S mints from the 20 are noted for weak strikes. This one may not be as bad as the 25-S or 26-S, but it is a far cry from the later ones.
It has a real nice strike and I can find only one nick. So luster is not its strong suit but it is still descent. The color is really more uniform than my picture makes it seem. Maybe it isn't the prettiest coin I have ever seen, but still not a bad coin. NGC called it a 64. I don't know what else to call it. It would be one heck of a 63.
I see very little holding this back from 64... which attribute of grading would your reference in calling it over graded.