I'm using Joomla to develop my website, and when I test my website on PageSpeed Insights on Google, it generates the following must-fix warning for me:
The problem with JCHOptimize is that it's hard to get it to increase your Google PageSpeed Insights rankings on your website without it breaking other stuff.
For the CSS, you will need to split your main CSS file to 2 parts: The first part is the one that you will absolutely need to make your website look well when it first loads (for example, the width of the
body), while the second part is the one that you can live without for a second or so (until the page fully loads).
In my opinion, trying to get something over 85 with Google PageSpeed Insights is overkill and is not really necessary. I know that most people strive for a 100, but for many, this number is technically impossible (we've seen it though on a few websites).