> Yes, my user-facing servers are proxying the files to the users.
I've never operated a service as large as yours, so take my question with a grain of salt: I'm wondering whether it would make sense to split off the actual file front-end servers from the user-facing servers (going for a redirect approach instead of proxying), since the requirements for serving the UI (low latency, low bandwidth) are so different from the file serving requirements (high bandwidth, but latency is not an issue). In theory, the traffic load from the files could negatively impact the UI latency leading to perceived sluggishness of the website. But perhaps that's not an issue in practice?
Since you mentioned elsewhere that you wanted to move to content delivery: What kind of content delivery do you have in mind? At the moment I can only think of either classic CDNs (but that's a few order of magnitudes larger) or ads (but that's an entirely different area).