I thought I should report back to this thread with my experience.
After the discussions above and a bunch of research, earlier this week I took a chance and bought a Kobo Aura One e-reader. It is 30% bigger than most e-readers (diagonal of 7.8" instead of 6"), with top end resolution (300dpi), and I hoped that would be enough to make the SR pdf readable if I zoomed in to the print area.
I'm happy to report that it has exceeded my expectations. I find the pdf quite readable without magnification. I have terrible eyes and am getting old, so have to wear fragging tri-focal lense glasses, so I assure you that the readability is not because of my amazing eyesight. Reading with no zoom leaves my eyes a little tired after an hour or so, but I can't go much longer than that reading physical copy without fatigue either.
I did install the KOReader 3rd party software (along with the associated 3rd party start menu for kobo, which lets you switch between the standard operating system and KOReader). It makes .pdf much more responsive, with faster rendering when turning pages or moving the page or even zooming. (I'm still playing with zoom options to try and find something I like -- unfortunately the easiest zoom modes in KOReader adjust to content size, but due to the dark footer across the bottom of the page this doesn't adjust to just the print size. But as I said, I don't find the zoom to be essential).
With this I've finally made it through most of Market Panic, finding it far, far, easier going than on a laptop.
And speaking of Market Panic, I was able to plug the Kobo into my laptop and just copy across my library of .pdf files like to any external drive, and use them right away.
As a side bonus, it comes built in with software that lets you very easily interact with public libraries for which you have a card (or at least, with a lot of public libraries -- mine is on the list, I don't know how complete that list is). So when I look up a book it finds it in their on-line bookstore, but also gives me an option to sign out the e-book from my local library if they have it (don't have to do two separate searches), and I've grabbed my first e-book and found reading it to be delightful.
On the downside? So far not a lot. It is a black-and-white screen, so the art doesn't come through great, but I can live with that. Bringing up menus so that you can go back to the table of contents or jump to another page is a bit slower than I'd like, as in it isn't near-instant but takes a few seconds. It does have a built in web browser but that seems pretty terrible and very slow, so most likely I'll do future drivethrurpg downloads onto a computer then transfer them over.
In short, I've been really happy with this one so far. Not the cheapest, but being just big enough to handle full page pdf was worth it to me.
YMMV and all of that, but I hope this helps someone else find an easier way to handle their books, too!