@j.p.s: That was mainly a 5 AM brain-xref because of the earlier CPU discussion ;D.
IIRC, that's a ~1.5MPix to ~2.1MPix jump (take that with a grain of salt, I'm terrible at maths ;D) from the Voyage to the KOA2.
Hard to tell where the difference might be: sheer pixel moving might? eInk speedups? More efficient text layout/rendering?
The only thing I can say if that the eInk controller saw a major hardware revision on the KOA2. But the different processor adds another variable to the mix
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