The day Jeremy Edgell, a co-worker at Classic, mentioned it was possible to checkout pull requests, I knew that this trick would greatly increase my code review efficiency. Jeremy's solution involved adding an additional reference to the pull request location in an individual git repo's .git/config file. You can see a similar example to Jeremy's Stash solution in this gist.
Checking out a Github pull request (Note: The git alias, gpr-origin, indicates the remote to reference. I have one setup for origin and upstream.)