[NiLuJe]

The ePub renderer is mightily awful as far as performance goes, especially on older FW versions.

The KePub renderer, on the other hand, has always been pretty decent, although still a tiny bit slower than a Kindle, which is especially noticeable if you've recently used one. Still perfectly usable, though (unlike the ePub renderer, IMHO, which was probably colored by the fact that I did come from a Kindle ;p).

With the recent tweaks (i.e., >= 2019.05), in KOReader, as long as you're staying in the default Portrait orientation, we're pretty much trouncing everything out there in terms of page turn speed, though, especially if you have a device with physical buttons, because you bypass a good chunk of the input loop/gesture detection/delay thingy that way.

Sidebar: turns out storage performance is also pretty key to some specific use-cases. For instance, I'd always found dictionary performance to be pretty meh on my H2O, while it's basically instant on my Forma.

The difference? A real eMMC chip on the Forma vs. the insane internal SD card design on the H2O. It's sure nice on the hackability front, but, man, is it awful in terms of performance.