Hmm, I'd actually change that to:
For reading books and comics - iPad Pro 11”
For reading books, comics and magazines - iPad Pro 12.9”
Comics (at least American ones) are typically 6 5/8" x 10 1/4" while magazines are often 8 1/2" x 11". Reading in portrait, magazines get shrunken down more than comics so sometimes, magazine font sizes can be a little too small for comfort on 10-11" iPads requiring zooming and panning.
Mind, the 12.9" is around same size as 2x 9.7" iPads side by side so it works well even for reading double page spreads in comics. Aspect ratio in 1/2 split view is 2:3 which is pretty spot on for comics so you don't get pillarboxing like you do reading in portrait on 3:4 iPads. Yep, I bought my 512GB 12.9 exactly for this purpose. Comixology HD comics can get pretty huge and you can certainly appreciate the extra sharpness and detail on the 12.9" 2732 x 2048 display. 😁