That's right, and because the compiler is only a (small but important) part of Arc, I can only do so much. Arubic, however, can potentially be a lot faster than Arc 3.1, because it makes many more changes to the language. But that's a different topic.
Anyways, the only real reason Nu would be slower than Arc 3.1 is because it wraps every global Arc variable in a function. This is so useful that I consider it worth the 5-10% performance hit.