You could always check out the sony prs-900, as people have been saying that it renders pdfs really well in landscape mode, it doesn't show the page all at once, rather you scroll through bit by bit and you can cut the margins out.
I have the sony 505 and I too use sopdf to read pdfs that don't reflow well on my reader. Most pdfs of journal articles and pdf books (academic) reflow very well, actually, so I don't have to use sopdf all that often. However, the articles I read are not graph-heavy, so that makes a difference.
You also might want to check out the Entourage Edge, which has a double screen. It opens up like a book, one screen is e-ink and the other is lcd, it sounds like it would be a good fit for you. I've linked the wiki page below.
https://wiki.mobileread.com/wiki/EnTourage_eDGe