I believe this particular problem is somehow related to an interplay between Evernote and Mac desktop OS X display drivers/graphics system.
The problem is extremely laggy in-line (in-note) display of PDFs and other embedded docs (Word, PP, etc.)
It's so laggy (constant pin-wheeling) as to render Evernote almost completely useless as a serious productivity tool.
The catch is that this is not an issue at all on any Mac laptop I've tested with - including an older, underpowered Air.
The laggy issue is on a fully spec'd Mac Pro (late 2013 cylinder model) with dual GPUs.
I've completely given up hope that this issue will be resolved. It's been ongoing over many revisions.