Since CQ is Java based application, You can use various JVM based performance monitoring tool.

Monitoring Page Loading Performance:

Page Rendering time debug. You can use control + Shift + U after page is loaded to debug load time for page.

In order to debug clientLib (JS, CSS) load you can use HOST:PORT/URL?debugClientLibs=true then you can use Firebug tool or access log to find load time for each js and css file.

Monitoring Performance using Java Visual VM:

You can also use java visual VM to monitor CQ performance. Since CQ exposes some monitoring data through JMX, you can additionally download JMX plugin for Visual VM to get more data.

In order to enable monitoring you can add -Dcom.sun.management.jmxremote in JVM param while starting CQ.

Some more tool that you can use to monitor CQ application.