Hardware-Requirements and Calculation rate

Hi
im new to cpanel but looks great, im on the search for new software and have tested ensim, confixx and need now some additional information! has anybody expirience how to calculate how much RAM / CPU / Harddisk i can calculate per site/account?

And how much accounts/sites could be handled with as example one server 2 x XEON 3.0 Ghz 4 GB RAM?

i havent found any details to that question in docu or FAQ, possible somebody in here knows!

thx for help

maxxx