Hi
I've been reading a lot of PDF on my inkpad 3, using koreader, and it works pretty well. I mostly read books and sometimes A4 articles, and if needed I cut the PDF file so that 1 PDF page = 1 book page as two pages in landscape mode would be rather small. For the file you linked as an example, with proper page separation it would work really well with an 8 inch ereader. (Once you find the proper software / commands separating pages is a rather quick process, and it's not needed for that many files).
The problem IMO with bigger ereaders is their pricing, but if you have the budget the latest Onyx Boox is probably a decent deal. Not sure how solid these are, and personally I'd rather avoid Android on an ereader.
You probably already checked the interwebz but I found
this article about ereaders and pdf reading interesting: screen size matters, but internal software matters even more...
Good luck, and please give your feedback when you've found the perfect PDF ereader.