Have you looked at Termite (that is, Gambit)? It seems to support continuations well - continuations are even serializable (along with ports, threads, etc) - and I think concurrency is handled exceptionally elegantly (built-in message-passing a la Erlang).
I never got many chances to use such exotic features, but I believe the combination of message passing and serializable continuations would allow you to do fun stuff like easily transfer code execution between different computers.
My limited experience suggested it was fast. It's also compilable to C. I suspect tail calls are properly handled - doesn't seem like something Feeley would let slide. I'm not sure about reliability.
I stopped using it because of lack of documentation and poor library support.
