Success! ~1200 accounts.

Steps:

1) Created temp VM on ESXi 5.1 server.
1) Added temp VM as new mailbox server to existing ZCS 7.1.1.
2) Moved ~600 accounts (~200GB) to new mailbox server.
3) Shutdown/removed old mailbox server (#1).
4) Installed ESXi 5.1 onto old mailbox server (#1) (now called ZVS1).
5) Created new mailbox server (ZVM1) running Ubuntu 10.04 on ZVS1 and added it to existing 7.1.1 system.
6) Moved ~600 accounts (~200GB) from temp VM to ZVM1 on ZCS1.
7) Created new MTA server (MTA1) running Ubuntu 10.04 on ZVS1 and added it to existing 7.1.1 system.
8) Deleted temp VM, removed it from ZCS.
9) Shutdown/removed old mailbox server (#2).
10) Installed ESXi 5.1 onto old mailbox server (#2, now called ZVS2).
11) Created new mailbox server (ZVM2) running Ubuntu 10.04 on ZVS2 and added it to existing 7.1.1 system.
12) Moved ~600 accounts (~300GB) from old mailbox server (#1) to ZVM2 on ZCS2.
13) Created new MTA server (MTA2) running Ubuntu 10.04 on ZVS2 and added it to existing 7.1.1 system.
14) Setup LDAP replication on ZVM1 and ZVM2, then transferred LDAP master to ZVM1.
15) Upgrade Zimbra from 7.1.1 to 8.0.1 on all servers.
16) Changed DNS records for new mailbox servers, and pointed MX record for round-robin to include MTA1 and MTA2.

LDAP changes and upgrade to 8.0.1 took ~4 hours. All of the mailbox moves were completed over a 1 month period (evenings & weekends) using the "zmmailboxmove" command.


Next steps:

1) Configure multi-master LDAP replication.
2) Install MxHero (once Zimbra 8.x is supported)
3) Update to Ubuntu 12.04 on all servers