Hi ,
Thanks for the feedback I'm really happy that you love them, they looks sophisticated,elegant and timeless stuff.
Anyway I think the best way if you keep them both , e.g you can give a dark header to your letterhead and that will works really good, also you can give a dark strip on a bussiness card that will give a strong contrast and a wow effect as well.
But as you seen that's likewise works on white as well because when I start to working on something like this project my first priority is that the concept need to works on both backgrounds.