I'm not a fan of MODBUS/TCP if it's riding the enterprise IP network. You're asking some very limited devices (limited relative to the rest of the network appliances) to manage a session based connection usually with a static set of parameters on a network that can be extremely dynamic. Not to mention that device is going to be exposed to things it was never designed for. Also, some implementations of MODBUS/TCP can cause real headaches with ID(P)S and session tracking firewalls.
There is the fact that MODBUS was never intended to reside in the hostile environment of current enterprise networks. It offers literally zero security, anyone with access to the network can read from or write to any available registers.
FWIW I'm a big fan of MODBUS. Its maturity and simplicity make it a solid process control protocol but you have to keep in mind when it was developed and what the original intent was.
Like Mr. BACnet previously mentioned I can't see any benefit if you only have one master. Is the JACE going to be located in the same facility? If so, I think you'd be better off using RTU and a dedicated field network.