I ran a quick test in Illustrator CC, and even though Illustrator uses a subset of PDF as it's own file format, when you go past 200x200" you cannot save your Illustrator document as a PDF. You would think that Adobe would add the capability to use UserUnits to Illustrator documents that are larger than 200", but that does not seem to be the case. I even tried to rename the .ai file to .pdf and to open it in Acrobat, but hat cropped the document to 200x200" (don't do this to create PDF out of Illustrator however, I am a professional on a closed course, and I know what I am doing :) )
So, it looks like you are out of luck when one of your dimensions is larger than 200".
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com