We're already faster than C in some benchmarks, (and slower in others, of course) and since we use LLVM on the backend, we can take advantage of all of the performance work that's put into Clang and friends as well.
I also forsee a significant speedup in complex applications caused by programmers being more free to do pointer gymnastics because they know that there won't be use after free or anything (as compared to using refcounting everywhere or a GC).
(http://manishearth.github.io/blog/2015/05/03/where-rust-real... has an example for others reading this thread)