Openfire crashes with 700 users in chat room

I have a openfire installation that goes really slowly when a room reaches 700 users. It can take a minute from a message is sent until users receive it.

I have installed the Java Monitor plugin and was hoping someone could take a look at the graphs and see if they have any clue as to what is happening.

The server running openfire has 8GB RAM and dual core.

I use 2 connection managers that lead the traffic to my openfire server.

Hope someone can take a look at the attachments

As you can see the problems occurs to the right in the graph… It works perfect for days, but when a room gets many users (over 500) it gets serious problems