Mike Pall's LuaJIT[0] is excellent from a game dev perspective--incremental GC (so you can spend a fixed amount of your frame budget in it) and JIT with a huge number of optimisation make it fairly compelling to write the top 50% of your game in (and not a terrible choice for the bottom 50%).

I think you were absolutely right to switch from Ruby, I can't see the problems that you had getting any better unless Ruby lets you manage object allocation (in which case you could allocate to a per-frame memory buffer and just nuke it at the end of every frame).

[0] http://luajit.org/

The cause of its popularity in the games community comes from the fact that it is, by design, meant to be embedded in larger programs. So, for example, it will compile on any platform with a conforming ANSI C compiler.

And for x86/x64 and ARM, you can try LuaJIT to get even more zing (though you probably won't need to).

Just because the Lua community will ream you out for the mistake (though it's the only thing they're mean about), it's "Lua" (Portuguese for "moon"), not an acronym. :)