If you wanna know a bit more on how luajit works and where it gets its blazing speed, here you have some links to explore it, and to get a grasp of differences between lua implementations.
Agentzh talking about why he (and cloudflare) are targeting mostly luajit:
Nice introduction to luajit. In fact it's mostly lua, but maybe the second part will be more targeted to luajit
And here it's a functional library which, not being directly linked to luajit, it makes a really nice usage of iterators to build code structures lazily and make the traces jittable by luajit. nice code read.