How Many Blogs Per Server

Hi,

For paid blogs where hosting performance is a selling point, what would be the ideal maximum blogs per server (based on multisite performance, etc.) to maintain optimal performance for all customers without compromise? Any advice would be appreciated.

Typical blog allotment would be up to 3 GB.

Server would be a current dual quad-core Xeon model with 16-32 GB RAM.

Thanks,

Mark