New install TDM2400P vs AEX2400 benefit from pci-express?


I am new to Asterisk but read a lot in the last 4 months…

I will use an HP ML350 G4p server, 2 Xeon, 2 power supply, SCSI Raid 5 with 3 x 76 gig disks. 6 gig Ram

I am not sure about which OS, Red Hat, Centos or Unbutu (any hints?)

Need 16 FXO and at least 4 FXS

Looking at TDM2400P vs AEX2400; But what is the benefit to put a PCI-express in instead of plan PCI.
Both cards meets my needs with room to grow (1 spare slot)

Plan to get with hardware echo cancellation… shoudl I ?

Am I buying myself problems or peace of mind?

BTW will serve 100 users in 4 sites plus some home workers…

So which card is my bet bet for stability, performance, service quality to users ?

Thank you