Quel langage pour une API REST web "haute performance" ?

The backend requirements I want to design are :

• High performance, request heavily externals REST or FIX APIs, like every 100ms or less. I understand multithread and asynchronous but probably not in depth.
• Need to be reliable, up 24h/24h but perhaps it's more a "devops" thing
• Will only serve few clients (ng2), lets say < 10
• Will use a relationnal database

So far I think about C#, Ruby and Nodejs.

1. Nodejs sounds gounds because the "dataflow" is almost completely async, it's apparently blazing fast but even with sequelize I'm afraid trouble could happen with relationnal database.
2. C# .net 4.0+ seems really mature and could fit assuming that it's really reliable for production.
3. Ruby looks like a happy medium, I heard good things about it but It's apparently more complex to make things right. I don't any any experience on it.

So given your experience, what language should be use ?
J'ai voulu poser cette question sur stackoverflow mais effectivement, dans les guidelines, celle-ci est "off-topic"... Si vous avez un avis, recommandation je vous remercie! :)