Those stats are normal. There are a wide variety of issues that can cause "slowness" for users. The ones related to system resource drainage are:
-Heavy load of "Perform Script on Server" scripts running.
-Server running other programs (EG shared drive, domain controller, DHCP controller, email server, etc..)
-User's hardware is old and having trouble running newer software.
-User is running too many programs on their computer
RAID 1 is ok, RAID 1+0 would be better.
Other things that cause "slow" are:
-Slow internet connections on the server or client end, including wifi drops and network changing.
-unstored calculations and summary fields
-the above, combined with large data sets (EG summarizing 50,000 records or summarizing an unstored calculation field).
Given your chart, it's something your users are doing, so you may want to see what operation they are performing when they report it's slow. It does not appear that something scheduled on the server is affecting it.