Sizing of large environment

Hi

Is there any Symantec recommended approaches to sizing of large (over 20 EV servers) environments? Easy way would be to have one EV server for each mailbox server (Exchange or Domino). But I have met situation when amount of items to be archived require amount of EV servers to be more (if rely on Symantec's value 90000 messages 70KB large on 16 cores server). I see no way to make 2 EV servers to archive mailboxes on one mailbox one. So alternative way would be to offload indexing activity to separate server or servers. But still I couldn't find any information, which would allow to calculate amount of servers and their hardware configuration (as Microsoft does for Exchange servers for example).