[danpalmer]

F# and Nemerle are both based on the CLR, and unfortunately the performance of Mono is pretty bad, and not really suitable yet for high performance use-cases like this.

Also I'd Erlang is state of the art, even though it is so old (Haskell too), but I wouldn't call it an entirely safe bet because it requires quite a different style of programming and experience, so might not work well for certain developers.

[CmonDev]

Isn't Erlang just a (semi-)functional language with Actor Model baked in? I might be wrong but it seems that you just need any dev familiar with message queues and functional style.