Honestly I don't think you'll be more productive at all. Emacs was fine as an editor a decade ago but a modern IDE--particularly IntelliJ of which I'm a big fan--comes with so much more than an editor, including a debugger, the ability to refactor your code, seamlessly move classes and packages, etc etc etc. A huge part of the productivity benefit of an IDE comes from those features rather than the editor.
If you're not using vi/vim as a primary text editor (meaning using it for significant development effort or just significant time) then whatever you use is ancillary to your IDE.
