They're hitting 35x in some benchmarks [2]. Most benefits being in workloads where Ruby has to continuously talk to C; the result-passing part gets compiled away.
It is available in Java 9, if I'm not mistaken. LLVM IR bytecode ingestion is in preparations too [3].
[1] https://youtu.be/b1NTaVQPt1E?t=48m17s [2] http://jruby.org/bench9000/ [3] https://github.com/graalvm/sulong