You still could benefit, because the optimizations are user agent-specific, and if you aggressively use caching with Nginx, then you don't need to make as many live calls to the backend to segment the cache per user agent type. PageSpeed is written in C and highly optimized so it has performance benefits in your case as well, I think. For example, there are user agents for which PageSpeed may decide to deliver your CSS as inline and small images - as data URIs. It also automatically (but optionally) does lazy loading of images, etc. It has beacons that are also implemented with it. It's perfect for CMS websites like it is in my usecase. It's not a panacea though.