asterisk users - Apr 2003 - (Hardware (processor) requirements / Performance

I've not used Asterisk before and, having found very little mention of 
performance in the handbook and the list archives, and wondering whether 
someone can give me some guidance about the below.

If I were to use asterisk as a bridge between a 30-channel PRI and 30 
H323 clients (using GSM compression), how can I work out how much memory 
and processor power I will need?  I'm hoping to be able to run multiple 1U 
boxes for redundancy, with each box being an entry-level rackmount server 
with 1 (zaptel-compatible) PCI card to interface to an E1.

Any comments/pointers would be appreciated.

Rahim.