I checked the Journal, and writing is practically instantaneous now on the lined background. This gives me hope for the PE where it lags noticeably.

I also checked a PDF ebook, and generally the ink flowed as I drew the line, but sometimes would pause for a second and then fill in that portion of the line before continuing. This behaviour suggests the CPU is busy and the ink has to catch up once the CPU is available again. This could be a background task, or it could be the reader app itself doing some processing of the ink.