Have you seen the new Swift 2.0 benchmarks that they discussed at WWDC 15? It's now getting extremely fast. It won't be long before it surpasses Rust.
Anyway, if 5% improvement is all that Rust will have over Swift, it's as dead as Lisp.
When Swift is finally open-sourced, there will be a huge exodus from Rust community and move to Swift. This is not survivable. Rust will quickly lose the little momentum that it has right now and it will be game over.
Personally I believe that any investment into codebases using Rust is a huge mistake and a waste of money at this point in time.