You haven't actually posed a question in your post!
Are you looking for comments on the figures?
There are so many places where the bad performance could occur but given that you never get a bandwidth more than 400KB/s when accessing over the WAN I would focus your attention on the components between the CRM server and the Internet. Even if you have
a high-speed connection to the Internet, the router/firewall and/or other network components could be the bottleneck.