asterisk users - Aug 2005 - RealWorld Stats; Not achieving expected results

Hey guys,
  We have a brand new Dell Poweredge 1850, Single Proc 3Ghz, 2GB RAM, 
15K RPM HD's RAID 1.

  We also have a Sangoma 4 port T1/PRI card.

  We are not using G729. Everything is G711.

  Every call is PRI -> Asterisk G711 -> Sip Carrier

  We just filled up 2 PRI's and reached a CPU usage of 70%.

  There's no way we can do 4 PRI's worth of traffic. Will a 2nd CPU 
really make that much difference? Why is there so much CPU used going 
from PRI to 711? I could understand 70% usage if I was using 729 but I'm 
not.

  I was expecting to be able to process 96 calls (all 4 PRIs) with about 
50% (or less) CPU usage.

  Any clues? Suggestions?

Thanks,
Matthew