Alright, I'm back. Busy life is busy.
Here's the stock PDF reader comparison:
https://www.youtube.com/watch?v=dips4v-1G3U
For this test file the differences aren't vast, although the M96 does seem to be marginally (a few tens of milliseconds) faster much of the time, and is significantly faster on graphics-heavy pages. The DXG, due to limited memory, isn't able to pre-cache pages as aggressively, and seems to prioritise forward loading, leading to more delays when flipping backward. The DXG also seems to do a full screen blank and redraw on each flip, whereas the M96's stock reader does it only every 5 (N.B. this is configurable), which increases the apparent time required to flip the page on the DXG.
DXG KPDF performance is similar to DXG stock performance for text, but significantly better when graphics are introduced:
https://www.youtube.com/watch?v=TzmpVolN97o
Comparison of zoom in DXG KPDF vs M96 stock:
https://www.youtube.com/watch?v=OuL2_Gxi-Vs
I'm hung up on the M96's stock reader because I haven't found a reader that both supports the forward/backward buttons (or at the least doesn't expect me to use taps - and therefore the stylus - to navigate. Do you flip book pages with a pen? Me either!) and doesn't have some other annoying quirk that makes it unpleasant to use. The best alternative I've found so far is ezPDF Reader Pro. It's definitely quicker than the DXG’s or M96’s stock reader:
https://www.youtube.com/watch?v=IUID2po2Oe0
On the minus side, it insists on displaying the (enormous!) Android status bar at the top, which eats some of the space that could be better used for rendering my reading material. In the file supplied, the result is that the text is rather on the small side and readability is strained. Moreover, this means that the effective resolution of the M96 is lower than the DXG, since more of the M96's pixels are displaying stuff that isn't document text. (First image) The effect is less marked in the M96 stock reader, but is still present. (Second image)
http://imgur.com/a/lFLKR
The DXG stock reader simply handles margins more efficiently, making better use of its screen. Sure, you can zoom in, but that’s a workaround, not a solution.
Also, for some inexplicable reason they decided to make an annotation overlay bar a feature of their program that, in the version available on the Play store, can only be disabled by a 5-finger tap— which is not a possible on this single-touch, stylus-driven display. After buying the app, I wrote to them to ask if there was any other way of disabling the overlay, but they did not respond. I obtained an older version of the program where you can still disable the overlay though a menu option, which is what’s shown in the video.
One thing I can't seem to do in the M96's stock PDF reader is move to an arbitrary page in a file. Can somebody fill me in how to do that? I tried tapping/D-pad clicking on the page number in the lower right corner - it does seem to be a selectable object if I navigate to it with the D-pad - but nothing happened. That’s a pretty serious oversight if it’s not actually possible.