IF I were to paint my center caps I'd scuff them up first for more "tooth." Then I'd use VHT epoxy paint. Not the high temp stuff, the regular epoxy black which I used to paint over the rear chrome trim piece on my Exp. Tough paint.
IF you want the benefits of a steel rim but want to avoid the "cop look" you may want to look at the Ford wheel covers made specifically for the PIU steelies. Ford supplies them as an option for undercover PIUs, it's a Ford part. I have a set that came with my steelies that I may swap out later.