From everything I've read Netty looks like a champ compared to all other NIO servers. :-)

So, I'm quite excited to have found the answer to my question, AND someone has already started a clojure/netty project:

http://github.com/texodus/saturnine

Check out these comparisons of Netty vs others:

http://gleamynode.net/articles/2232/

http://amix.dk/blog/post/19456

http://www.znetdevelopment.com/blogs/2009/04/07/scalable-nio...

http://www.znetdevelopment.com/blogs/2009/04/09/scalable-nio...

http://www.znetdevelopment.com/blogs/2009/04/13/scalable-nio...