This year we have added another 1000 student laptops to our school and Moodle performance instantly took a beating, with CPU load hitting and holding 100% for an hour at a time and pages taking over 5 to 8 seconds to load. We upped the CPU's cores available to the front end server from 8 to 12 and then to 24. Now at 24 processes things are moving along much better.
One of the things we have noticed is that if we use IE the pages load in less than 1 second, but if we use Chrome (under the same circumstances) the page takes about 3.5 seconds to load. Yes 3.5 seconds is not long but it is long when you are sitting there waiting to do things. So if IE loads in under s second, I would believe the server is running fine and it is either something to do with Chrome-IIS, Chrome-PHP, or Chrome-Moodle.
RAM and other areas look fine.
Front - Windows 2008 R2, IIS, PHP 5.6.0
Back - Windows 2008 R2, MySQL 5.6.19