Thanks Francis,

Yes I suspected that it was somehow renegotiating the ssl handshake for each request where as firefox/firebug was caching the handshake thus showing quicker response times.

Timing curl over https gave me an average of 80ms response time, timing curl over http gave me an average of 10ms similar to what nginx was achieving talking to the backend via http.

I'm happy to annouce though that your were bang on the money with the keepalive directive. As soon as I added that into my upstream declaration the reponse times dropped considerably and I'm now getting performance similar to as if I was requesting the content directly from the upstream server.

Thanks Francis your a legend :)