[Asterisk-Users] Confused --> Hardware specs

[Asterisk]

Having kept an Eye on hardware specs mails in the list, and having read the
hardware notes on voip-info, I am still confused over the recommended
hardware:

We are going to have up to 100 operators and staff making calls, mostly
through zap connected to TE405P through to a 32-channel E1. However, it is
possible that we may need another E1 - what is the rough ratio between
operators and calls when the call length on average is 3 minutes?)

I was thinking of adding some VOIP into the mix. So, what speed proc should
I use ? I am currently looking at:

A) Dual-Xeon 2.8 with 2 GB ram and 36 gb raid-1
B) Single Xeon 3.0 with 2 GB ram and 36 gb raid-1

So, assuming I stick with 1 E1 line, is a dual better than a single, or
should I take the savings from buying a single Xeon, and buy two machines
with two TE405p cards ?

Help!

Thanks.