I don't think you have to sacrifice any meaningful amount of productivity to learn Vim. Contrary to popular opinion, I think vim has a pretty smooth learning curve to begin editing with it.
It might take a bit more effort to learn than, say, Sublime Text or Atom, yet after playing with "vimtutor" and reading a blog-post or two, you can learn how to open a couple of files and display them in splits, how to do modal editing, search, replace, copy/paste[1], undo/redo, save and close in a vim buffer. It's basically everything you will need to start using vim as your primary editor and it can be learned in a couple of hours.
After that, you can always learn deeper aspects of vim later and customize it in a leisurely pace in weeks to come.
It might take a bit more effort to learn than, say, Sublime Text or Atom, yet after playing with "vimtutor" and reading a blog-post or two, you can learn how to open a couple of files and display them in splits, how to do modal editing, search, replace, copy/paste[1], undo/redo, save and close in a vim buffer. It's basically everything you will need to start using vim as your primary editor and it can be learned in a couple of hours.
After that, you can always learn deeper aspects of vim later and customize it in a leisurely pace in weeks to come.