DCC server or Client suite to us?

Hi ,

We have got Sendmail + Mimedefang + SpamAssassin with DCC+RZOR set up
on Solaris running as mail gateway. Current installation is 2 years old
and I am thinking of upgrading it. I wanted to know the right DCC set up
for our system. 

We have got four mail gateways - Total mail per day on four gateways
together is 400,000 to 450,000 (50,000 -100,000 outbound, 300,000 -
350,000 inbound)

Should I set up our own DCC server or can I use the public dcc servers?
Can I do it on one of the gateway? If I needed to set it up on one of
the gateway, how can I set it up so that all four mail gateways can use
it?

Thanks
Mathew