Unbound optimization

Hi all,

Need some hints on how to configure unbound for an ISP environment (Proof of Concept). 4 high performance servers will be running FreeBSD 7.1 with 8GB RAM and 4x72 GB SCSI. The number of users is around 500,000. I am looking at 250,000 concurrent users (Peak time). Servers will not be authoritative, just act as a recursive and caching dns server.

Thank you
Monah