pubsub: Why is .send() 10x slower than .publish()

I have a server on EC2 with openfire and use pubsub to send messages to it

If my smack client uses node.publish() I can send about 150 messages/second (which might be the limit of my laptop...).

But if I switch to send using node.send I never get more than about 5-10 messages second.

Why is it so much slower?

I would expect some slowness but not that much. Is send so much heavier on my client or did I miss something on the server side? The server has plenty of spare CPU, memory and IO while sending from my client in a tight loop.