More on the USB-Serial Issue
The USB Serial device that has given me a problem is the IOGEAR USB to 2-Port Serial RS-232 Converter, Model GUC2322. I reinstalled it and reinstalled the driver on their web page. Again I noted the major increase in the System Process CPU usage. I removed it and placed an old USB 1.1 Prolific adapter in and the CPU usage for the System task went to 7% on the peaks and stayed down at zero most of the time.
I will eventually contact IOGEAR and Moschip to find out why. But for the moment the Dual Port device is not usable in my system.