XML is getting close to being a 'universal' translation language for PLCs however not all in "XML" is created equal either. As an example GE Proficy ME can also Export/Import .xml how ever try Importing an xml from AB and it is rather interesting.
The problem with "Plant Specs" is that they are always out-of-date and too restrictive. Whereby you end up with old controls on your new equipment or only the cheapest your "Spec" dictates instead of the best for your new equipment.
I have a lot of experience with these and recommend them:
http://www.geautomation.com/architectures/quickpanel-control-system
There are several sizes and price ranges all use the same I/O, drivers and software. Very reliable. The only down today is that for Ethernet I/O it is only Modbus TCP/IP...
The letter at the end of those part numbers designates a revision of the hardware. There will be no difference in their operation or configuration.
If there are two letters it usually is that one letter is firmware the other hardware.
First make sure that all of your CPUs and Ethernet modules if used have the latest firmware. If that does not help the situation get a monitoring software like www.Wireshark.org to try to narrow down where the problems are coming from.
I would bet on the cabling be it FO or CU.
No but I have a recommendation, if your projects are of any importance use something that can still be serviced.
If not important maybe use one and keep the others as back instead of servicing the one used.
Most of the "brand" named HMI's are reliable today but of course they all have a few 'lemons' from time-to-time.
However I highly recommend that if it is at all possible your system should be designed in such a way that your machine or process can be run without it in an emergency.
It is generally best to check with your insurance carrier to verify what they need to cover the system in case of failure.
If you are self insured get a write-off from your boss whoever that is and file it.
If you are not insured, put in series two over-temp devices.
