Radiator Paint Question

I recall reading in one of Dan's books that steam radiators painted with metallic paint (silver or bronze) will give off 10 to 20% less heat than those painted with nonmetallic paint. Several of my radiators have been spray painted silver metallic. To switch to nonmetallic paint do I need to strip the silver paint off or can I just paint them over in white or black? Cosmetics aside...is this worth the effort.