Speaking for myself, this is not at all about page load times.
For us, we do like to work in an environment where you can quickly jump from section to section without too much clicking around. In this regard Evolution is a bit slower to work with. When you are administering a bunch of servers a...
You could also allow your resellers to make use of the CSF interface to unblock the IP addresses of their users. You can set this up if you head to CSF > Edit Reseller Privs near the bottom of the page.
Perhaps MySQL is acting up?
You can use mysqltuner to see if it requires more RAM or some performance tuning is needed.
ps -aux will display a list of running processes along with their memory and CPU usage
or building on that ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%mem | head
htop is indeed...