Hardware for Asterisk

Can You tell me something about server which I should buy for my Asterisk CallCenter.
System: 4xE1. Now I have very cheap solution 4xE1 Digium Clone. But I cannot longer manage with this equipment. Database is located on the stronger computer.
I want to buy Sagoma or Digium. Which one I should to choose ?

Server I can choose between Xeon or Opteron. Which CPU will give me better efficiency ?
Now I have ( silly ) Celeron 2,4 with 256 RAM and when more than 32 calls occur it’s a big problem. It hangup calls.
I have 15 agents ( 3 voip and other standard phones ).

System Architecture: Admin Clients, Phone Clients, Asterisk ( integrate with MD100 or PB250 ), CAGI programs ( my scenario dial ) - connect with database.

My system works for about 6 months, I am doing it for about 9 months.

10 thousand people can call to my call center.
I will be very greatful if someone give me some advices or tips.



More power, more RAM.
I prefer Intel processors. I prefer Digium hardware - they developed Asterisk, this should mean their hardware must work better with Asterisk, but I have no experience with Sangoma.
If all your calls are SIP - you can use SER.
If not - try to use only one codec, and no compression.
There are a way to make somthing like cluster - a couple of servers with Asterisk to work like one computer.

I think RAM is not so important in this architecture ( Asterisk and 4xE1 ).
More important is time of CPU answer. I have only 2 SIP phones. Other phones are old one.
Cluster ( i do not know how it could handle ). It isn’t better to keep all asterisk’s process ( and controling process ) at one computer ?
Few years ago I was testing OpenMosix cluster. As I remember not every program work with mosix. Asterisk ? I do not know what effect it will bring.

You can get clues if you will take a look AsteriskTFOT.pdf
There were some clues what to do if you will need real power.