I just ran across this article on Groovy++ performance. Groovy++, it turns out, is a project to implement a static compilation of Groovy. This article reports a 6x performance boost for the low price of adding a few keywords. Very few, it turns out. We're not talking manually defining all of the static types, as in Java, but in telling the Groovy++ compiler to fix the types during compile/runtime. I'm hedging with compile/runtime since, honestly, I only discovered this project a few minutes ago and haven't had a chance to really dig into the details of how it works. The project is hosted on Google Code and, although it isn't open source yet, it's slated to become open source soon. A decent introduction to the developer and the rational can be found in this article.
I'll have more to say about this once I get a chance to really check it out, but in the mean time it's something worth watching.