BOSH versus native XMPP over TCP

I have a questing related to the number of clients / load capabilities with BOSH versus native XMPP over TCP.

As far as I understand BOSH requests go through an embedded Jetty HTTP server before the reach Openfire’s XMPP server engine. Does anybody know how the HTTP processing in Jetty decrease the number of clients / load that an Openfire server can handle (rules of thumb, like 50% or so would be very welcome).

I know that Jetty allows asynchronous client connections (via continuation). Does Openfire use this, or do I have to expect that each BOSH client needs a thread in the Jetty server to receive the incoming data of a chat. This would mean that the number of threads might be a limiting factor.

Any link to related discussions is also welcome.