Reaching a 100% score is a bit hard and most likely it's not enough to just use a plugin, additionally it is also directly related to server performance.
However, in most cases you can reach a score above 90, which is an optimal and perfectly reasonable result, remember that Google will mark sites as 'slow' if they have a score less than 50.
Having installed JSpeed with all optimizations enabled on an average server, several websites have been escalated from a score between 40 and 50 to a score greater than 90.
To reach a high score with a Joomla website on the Google PageSpeed test, you should take care of the following best practices, all obtainable using the JSpeed plugin:
- Minify stylesheets: it's important to reduce the size of CSS files as much as possible
- Minify HTML: the page source code can also be minified to reduce the total size and bandwidth usage
- Optimize images: avoid to use heavy images that increase a lot the total page size
- Use lazy-loading: images and iframes that are out of views can be loaded only when the user scrolls down the page to reveal them instead that on the page load
- Take advantage of HTTP/2: the second version of the HTTP protocol includes several enhancements such as the preloading of resources
- Use a CDN: you can setup a CDN service of your choice and make all assets loaded by Joomla to point to that external CDN instead that to your website
All these aspects can be addressed by the
Joomla plugin JSpeed, as a result you can be able to reach a very high result in the Google PageSpeed test: