Model Ms are great, but now that I have a Model F 122-key terminal board (actually 3 of them) working with Soarer's Teensy process (and some keys remapped (how will I ever fix NumLock and Pause?) to simulate something very close to the standard M layout), I have to say that they are the cream of the cream and I am utterly spoiled.
I recently did a primo meticulous bolt-mod on a super-clean 1390131 that came out magnificently, and was thoroughly enjoying the King of Keyboards until a couple of days ago when I went back to the Emperor of the Galaxy, and I have to say that there is no contest.
Everything about the F is on a whole different level, sound, feel, weight, the only downside is the acres of footprint that it occupies.
My F AT is nice, but I really use the Numpad, home cluster, AND arrow keys, so the small layout just doesn't work for me.
For me, the effort of the conversion was easily justified to get the capacitive switches (I don't game so the NKRO does not mean anything to me) and the exquisite light feel, but I would not bother with a 122-M conversion, because I look at the "classic" M layout as the ideal. Of the 20 extra keys, I really like a second F pad on the left, but the others are just toss-offs like "Mute"