The key thing I noticed in the relative study is also that they said people experienced literal amnesia about the additional time required to choose a shortcut.

I'd be interested not only in a better study of the effect of expertise as well as looking at the effect of this "amnesia" on productivity. Even if it takes me longer to do a task in Emacs, that amnesia suggests that the interface is less distracting, which might be far more valuable than speed.