I looked at those files again using the El Capitan Gold Master running on a Late 2012 Mac mini with 16GB RAM and observed none of the problems you experienced. I could scroll freely from the top to bottom and left to right margins and without a SPOD using Preview 8.1.
However — there is definitely something funky in the PDF construction of the file. When I opened it with PdfPenPro 7.3. PdfPenPro was slower than Preview 8.1 opening the file and I did get a couple of brief SPODs while scrolling around the document, but there is a second pane on the left side of the widow containing what appears to be a duplicate copy of the document. I cannot determine if it is a duplicate or not as it is displayed too small to read and I was unable to zoom in on it. Weird stuff!
I opened the document in Adobe Acrobat X and it started out with a black screen and then turned blank white. The scroll bars indicate it is scrolling up and down, but nothing the display remains blank white.
I do not believe the problem is with your iMac, Yosemite, Preview, or Adobe Reader rather it is something in the structure of the document itself. I would be tempted to speculate that it is a result of one of Adobe's proprietary PDF features that has not yet been released into open source but I downloaded Adobe Acrobat Reader DC and like the much older Acrobat Pro X it just came up with a blank window. Frankly at this point, I am amazed that Preview 8.1 can handle the document. Some Apple developer(s) deserve(s) kudos for that.
