While sometimes it's great that you have the option to use C bindings in Ruby, my take is that if possible you should write stuff in Ruby when doing Ruby. If that's not the case you are not doing ruby, you are doing C.
I would write clojure and drop back to java for speed. Only in a extrem case I would then use C, but its possible. I haven't done it but read that its not all that bad. (there is a clojure wrapper.