Simple steps, have you tried running the machine(s) locally (unplugged from the network)? If so do you experience the same/better/worse speed from CAD? If the speed increases when handling files locally we can assume that its a network issue.
So we move on to:
What spec is the server running the storage/Licence files? What speed is the network (i.e. 10mbps/100mbps/1000mbps) connection? Are the CAD machinces in a seperate network or VLAN? Has the admin imposed a bandwidth limit within your network to even out the throughput?
stu