" Probably, this is the maximum for the 13.3 Carta e-ink matrix."
I think that you can squeeze out much more from Carta, Dasung's new Paperlike hd seems blazing fast!:
https://www.youtube.com/watch?v=OO0Qzuw18q8&t=25s
(don't want to spam Onyx forum with Dasung)
So there is a room for improvement on the software side most probably.