I transfer files to the pi via owncloud, it is incredibly slow on my pi 3b
Just guessing, are you using ethernet and does the Pi 3b have drives plugged in to USB?
A big issue with the Pi 3b is that the ethernet and USB share a single channel, so if you’re writing to a USB drive then you’re bottlenecking your ethernet and vice versa.
You could try using wifi instead of ethernet. I’ve squeezed out some extra performance in the past doing so.
To answer your question though, the Pi 4 does remove this limitation so you should see much higher throughput than the 3b
Presumably they wouldn’t necessarily know the 2nd server even exists if they’re just hitting the reverse proxy. As long as both the reverse proxy and the origin server aren’t under the same VPS provider I would expect that to be fine.
Reverse proxy gets targeted, shut down, you spin up a new one somewhere else and keep going.