One other recommendation I'll make is on the device configuration, be sure to leave the maximum concurrent requests at 2 (seems to be the sweet spot for me), but under advanced, change the connection size to 4000 bytes instead of the default of 500 bytes unless you're talking to an old processor through like an old ENBT card.
@pturmel also has a great driver that is much faster than the built-in driver, but that all depends on if this is Ignition Edge (custom modules like his can't be used on Edge). While it is an additional cost, if you're not able to change the structure of the PLC to get faster comms, his driver may help.
@pturmel I'd b curious about the 4000 byte connection size and how it relates to MTU size of ethernet considering this is larger than the default MTU of 1500 bytes. Do packets get fragmented, or do both ends automatically know to break up the request into multiple packets?