I'm not sure if there is a 'best practice' around it, but my reasoning is that the NewRelic::F5Plugin::VERSION is the source of truth for releases.  Specifically, when I create a new release the rake task grabs that value and inserts it into the spec file (so it must always be updated).

Beyond that, it is just a little cleaner code wise, as you don't have to load the gem specification out of the file.