I don't think those two cases are comparable. Ruby is a fairly large and very generic language. It's possible to override pretty much anything, which makes run

I don't think those two cases are comparable. Ruby is a fairly large and very generic language. It's possible to override pretty much anything, which makes running it efficiently on a runtime that doesn't is hard. On the other hand, JVM bytecode is a tiny, concrete language, pretty much just saver assembly. Few operations are generic, and when they are they're generic on the type of something, not much else. Most languages that are already fast could probably run translated JVM bytecode fast. (And of course LuaJIT is amazing, but for being that fast in the first place)