I don't really like it when servers are over loaded but you really can't do much about it but back up and move to another host, or kindly email them and see if they can move you to a new server since the servers are overloaded. I don't think I have ever overloaded a server in aspects of clients... I have over loaded it of a damn CGI script, at a certian time this script would run since it didn't run off of Mysql and would just take about 30% of the server which was nothing really on the servers we had...
If you have an issue of overselling just ask them kindly of moving you to a different server they have and if they say tough, say "Thank you," and then cancel after you have backed up and moved to another host.
3 cents