In the old days, when the color of your credit card meant something, I believe the classic card was $60 and the gold card was $100. Premiers and above, however, could get the gold for the $60 (as well as not having a monthly cap on miles). I still have a gold card but I'm under the impression the standard offer is now platinum for the $60 fee. So the old discount is now irrelevant.

As an aside, there was (and I think still is) a significant incremental benefit from the gold having car rental insurance while the classic did not. I think the differences between gold and platinum are inconsequential.