Yes, it can be set to 100ms. I have mine set at 50ms, but I'm using an ethernet connection. I'm not reading a large amount of data in this application. I had some other applications where I had to add a checksum calculation to groups of 100 registers. I was stripcharting blocks of around 1000 registers. I had to make labview read until the plc checksum matched a checksum calculation in labview from the data that was read from the opc server. I was using Modicon Momentum plc's with Ethernet and Kepware. I setup the data transfer using IOscanner in the plc and Kepware as a mailbox. This made the plc push the data into the opc server without Master/Slave requests.
If you are using a serial port, it may depend on how the data is grouped in the plc. One read of a large group of registers, will be much better than several reads from data that is spread out all over the place.
If you are using ethernet, you will not want it tied into the corporate computer network. A dedicated network to the pc will be best. You can also multihome an ethernet card and give it multiple ip addresses. They work independently.
