First, your quality of life isn't really a selling point from employers point of view. To raise your odds at negotiations you should focus solely on the employers problems. The same applies when selling something - you should not focus on the benefits that you as a seller get (like money), but on the problems that get solved from the employer.
Secondly, focusing on raw productivity on alone seems to be quite a common thing on these discussions. I think it is quite limited viewpoint, since a ton of other things matter as well in addition to productivity. Communication with others, spreading your knowledge, trust issues, where to focus, etc.
