I have an iPad Pro, daylight and remarkable 2. iPad Pro is definitely the fastest. The daylight and rm2 are slightly slower and I do notice it, but they are definitely fast enough. The RM2 is the slowest and that is just e-ink physics at that point. I was pleasantly surprised by the speed of the daylight when I used it.
It's all lost on me although, since I don't really like pen input. I find the RM2 frustratingly slow for an epub e-ink reader. Compared to a kindle or others it's weirdly slow, even when pen input is fast. The daylight solves the outdoor computing problem for me.