[Dovecot] What is normal CPU usage of dovecot imap?

[Mikko Lampikoski]

I got Dual Core Intel Xeon CPU 3.00GHz, over 1000 mailbox and almost 1 dovecot login / second (peak time).
Server stats says that load is continually over 2 and cpu usage is 60%. top says that imap is making this load.
virtual users are in mysql database and mysqld is running on another server (this server is ok).

Do I need better CPU or is there something going on that I do not understand?

# dovecot -n

# 1.1.11: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-4-pve i686 Ubuntu 9.10 nfs
log_timestamp: %Y-%m-%d %H:%M:%S 
protocols: imap imaps pop3 pop3s
listen: *, [::]
ssl_ca_file: /etc/ssl/**********.crt
ssl_cert_file: /etc/ssl/**********.crt
ssl_key_file: /etc/ssl/**********.key
ssl_key_password: **********
disable_plaintext_auth: no
verbose_ssl: yes
shutdown_clients: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/lib/dovecot/imap-login
login_executable(imap): /usr/lib/dovecot/imap-login
login_executable(pop3): /usr/lib/dovecot/pop3-login
login_greeting_capability(default): yes
login_greeting_capability(imap): yes
login_greeting_capability(pop3): no
login_process_size: 128
login_processes_count: 10
login_max_processes_count: 2048
mail_max_userip_connections(default): 10
mail_max_userip_connections(imap): 10
mail_max_userip_connections(pop3): 3
first_valid_uid: 99
last_valid_uid: 100
mail_privileged_group: mail
mail_location: maildir:/var/vmail/%d/%n:INDEX=/var/indexes/%d/%n
fsync_disable: yes
mail_nfs_storage: yes
mbox_write_locks: fcntl
mbox_min_index_size: 4
mail_executable(default): /usr/lib/dovecot/imap
mail_executable(imap): /usr/lib/dovecot/imap
mail_executable(pop3): /usr/lib/dovecot/pop3
mail_process_size: 2048
mail_plugin_dir(default): /usr/lib/dovecot/modules/imap
mail_plugin_dir(imap): /usr/lib/dovecot/modules/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/modules/pop3
imap_client_workarounds(default): outlook-idle
imap_client_workarounds(imap): outlook-idle
imap_client_workarounds(pop3): 
pop3_client_workarounds(default): 
pop3_client_workarounds(imap): 
pop3_client_workarounds(pop3): outlook-no-nuls
auth default:
  mechanisms: plain login cram-md5
  cache_size: 1024
  passdb:
    driver: sql
    args: /etc/dovecot/dovecot-sql.conf
  userdb:
    driver: static
    args: uid=99 gid=99 home=/var/vmail/%d/%n allow_all_users=yes
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth-client
      mode: 432
      user: postfix
      group: postfix
    master:
      path: /var/run/dovecot/auth-master
      mode: 384
      user: vmail