dovecot - Aug 2014 - About network throughput between Director and backends

I plan to migrate my Dovecot IMAP servers to a clustered structure. I'm 
planning a cluster with high availability and load balancing.

I know I need instances of Dovecot Proxy / Director. But these instances 
can be on another network? There is need for high network throughput 
between the Director and the backends?

For me it would be cheaper to run Director in VM's at Amazon AWS for 
example.

Thanks!
--
Thiago Henrique