Hey Tim, I used the Windows Performance Monitor tool and watched the CPU when the system was struggling. To my surprise, the CPU utilization was less than 5%. Now before I enabled Opcache, the CPU utilization even for a single user was 70 - 80%. I did turn on the performance tracking under Admin--> Development-->Debugging so I will see if that reveals anything. I will also try your suggestion of installing some profiling software.
I have also read on other posts that I shouldn't be using Apache with Windows Server. I should use IIS instead. Just for grins and giggles, we have stood up another Moodle site and configured it to run IIS.