one reason why BC CC is better with metalics is how they lay. No matter how good you spray a SS metallic it will always look like the flakes are two dimentional, but with BC CC they appear to have depth to them and aren't just standing on one level like on a piece of paper, and that's what SS metallic looks like. Also, you're trying to get your flakes to lay right AND have a decent gloss and peel. This makes it difficult when you add the fact that you don't want to do too much sanding on buffing on SS metallic cause it will bring the flake to the surface and then it will look like a fish was scaled on your car and cleared over. BC CC is much more forgiving in the spray process, will look better (metallics), and last longer. So if you put considerable time in your project might want to consider that. Just my two cents.
Single stage solids are a different story.