"Proper" Benchmark to Determine Hardware Needed By Call Volume?

Hello,

Does anybody know if there is a benchmark that exists to show how many calls a current set of physical hardware could potentially maintain, and also how many calls a theoretical set of hardware could handle?

I need to know just how expensive of a unit we would need for call centers, etc. without overspending on something that isn’t necessary.

Thanks guys,

Jon

http://letmegooglethatforyou.com/?q=asterisk+dimensioning

first hit?