Try to move through the pages, don't stay on the first one! I have the 22nm i7 CPU here and compared to the work with Adobe PDF reader it's just horrible having to use pdf.js.

I must however admit that I'm not able to easily construct a Google search for more such documents, but I know a lot of people who work only with such -- they just can't work with pdf.js.

Does your benchmark measure the time to actually display everything on every page (what the human looking at all the pages must do), or just the time until the browser is responsible?

Edit: inspired from other comments, it seems that at least search for "math plots filetype:pdf" returns more guaranteed problems like

http://www.engageny.org/sites/default/files/resource/attachm...

Still it's hard to find slow PDFs with certainty just by using Google.