It is definitely one of the cheapest ones. Under label you only have TextBase, but unless you're really pointing out for max performance, start with your original idea: Label with spark BorderContainer.
If you want to go a step further you would be using flash and draw the movie clip yourself. But at that point if you ask me, you're loosing the benefit of using Flex in the first place.
Hope this helps, go with your idea.
Cheers.