well the XServes would be used for authentication (creating network users), file sharing (multimedia files, etc) and shared libraries (applications, etc)
A fiber link should be LAN speed or greater, so bandwidth and response should not be a problem. You can also use QoS in the network to prioritize multimedia traffic if necessary.
If Open Directory is configured, I would make one server the OD Master, and the 2nd a replica -they will sync across the fiber links.