Hey Don. You've likely seen pictures of my Camaro nose el camino before. It has parts in both bc/cc , ss, & ss/cc, though none is spi yet. From pictures you can't tell, & when all clean & buffed it's still hard to tell. But as Jim says, when they age;;;;;;;;;;. The single doesn't stay as clean with age, but can look truer black in some lighting.
I'm personally starting out next with the black spi ss myself, as I'm doing more metal mods than I have time for & need to complete sections in stages as time allows, rather than repaint all at once. For a new complete paint job, I'd agree all ss or clearcoated. Another thought though if you're not trying to bury the stripe outlines under clearcoat & sanding, you could try stopping the clearcoat line right at the outer stripe. then sand just enough to flatten most of edge & buff all together.
By the way, you talked me into just checking out this site for myself on a pro-touring .com pm when asking you an spi question, so thanks for that. Been my new favorite site.