https://docs.google.com/spreadsheets...true&sle=true#
That is a document that tracks throwing velocity at the combine back a few years. According to the author if you throw less than 55mph, you are pretty much destined to fail in the NFL. Higher doesn't guarantee anything, but gives you a fighting chance.
For those of you looking for an "I got you" - Dak Prescott supposedly threw with an injured shoulder at the combine.