[MarjaE]

I think I finally found a way to pre-check which pdfs are likely to take forever on my Kindle, or other slower devices. [P.S. gtime and gs are gnu-time and ghostscript.]

gtime -p -o input.pdf-timed.txt gs -dNOPAUSE -dQUIET -dBATCH input.pdf

In Mac Automator:

Application recieves files and folders as input.

Run Shell Script.

Set to use bash and recieve input as arguments, then:

for f in "$@"
do
suffix="-timed.pdf"
base=`basename "$f" .pdf`
outputfile=$base$suffix
/usr/local/bin/gtime -p -o "$f"-timed.txt /usr/local/bin/gs -dNOPAUSE -dQUIET -dBATCH "$f"
done

It outputs a txt file listing how long it took for ghostscript to run through the original file. I don't think the suffix, base, and outputfile lines are actually needed.