1. I did some quick tests and couldn't find any significant difference in speed or disk usage using --depth,
2. Why peg to a specific version now? I normally test gems / plugins with the latest of everything and then peg if something breaks - since the users env will vary - I think its better to know it works with the latest versions (Applications are different - there its best to commit the Gemfile.lock and control the updating, with possibly an extra test in CI that removes Gemfile.lock and checks if the latest gem versions break things)