MageStack offers native support for Google Pagespeed and it can be enabled with a simple addition to your ___general/example.conf configuration file.
pagespeed on;After that, you can define any of the Pagespeed supported options, you can find a detailed list of those here and an optimised list here.
As MageStack runs Nginx, you should use the Nginx syntax for Pagespeed options,
Eg.
pagespeed on;
pagespeed EnableFilters prioritize_critical_css;