After my failure
adapting Sailfish to my old Xiaomi phone, I decided to instead order a new battery for the Xiaomi and install Lineage OS on it without Google services. Then backed up my OnePlus X, and installed the latest Sailfish image.
While version 3 of Sailfish is just as fast as the early version, it still suffers from the same major issue (as far as my usage goes). That issue being the native Sailfish applications are either too simple, outright horrible, or non-existent. To make up for that, one would assume Jolla would put extra emphasis on the quality of the web browser. However, the Sailfish browser is a hot mess. Extremely slow, and often enters situations where you are not sure if you clicked something, or it's just stuck. At least the good news is that Jolla are working on a new browser.
I'll write a bit more in a few days after I have lived with this build for a bit.