I understand it's best to not bury strings in the nut, that the string slot depth should be about 1/2 the string diameter so that the string appears to be sitting almost on top of the nut (let me know if that's incorrect).
It would seem to me (who's not done it, but wants to) that the proper way to reduce string height above the first fret is to take material off the nut's bottom, and leave the slots alone. I've got new guitars with original nuts that appear to be done this way, and which are reduced more on the treble side to get those strings closer to the fret, so the saddle appears a bit tilted down on the treble side.
Notwithstanding that assumption, I see pros regularly deepen the nut slots, eg
http://www.bryankimsey.com/nuts/nuts3.htm to adjust 1st fret string height.
What's the best drill on this process?