Sorry - my mind was on LED display boards hanging on from the ambiguity of the first post...
The number of pixels to generate/render is the same.
ePaper may be a blessing, as I believe it's refresh rate is fairly slow.
I've never used it, but the driving circuitry may be another consideration.
These two links may be interesting...
http://spritesmods.com/?art=einkdisplay
ePaper driver theory