Hi Nicolas,
T1/Machine is not a real bottleneck if you throw enough hardware at it. We're running several configurations of Centos/Asterisk with 24 AudioCodes based E1 channels and Software-SS7 here.
Configuration is 10 GB Ram and 8 procesor cores. The machines are sold preconfigured like this under the 'TREX' brand by www.carrier-connect.com.
What kind of HW is the machine ? You realy have 10 T1 on one machine ? How does that scale ?