As somebody who shot film for 40 years, I've got a reflexive urge to say "yes" to fast lenses, but I'm now losing that reflex. In terms of low-light shooting, I'm happy enough (with my style of work) to go to 3200, or even 6400 if I have to, which makes up for a lot. I know some people like the shallow(er) depths of field that you get with fast lenses, but my feeling about that is that when I'm looking for really shallow depth of field for some good reason, there are always prime lenses. I can't think of the last time I needed shallow depth of field for a snap shot, where I wouldn't have time to change lenses, and I'm usually carrying a fast 85-equiv when I'm out (Panasonic LUMIX G 42.5mm f/1.7 ASPH.) In fact, it's often already mounted on a second camera. The point being, if I were to get into the Nikon Z system, which is somewhat likely, that 24-70 f4 looks very good to me. I wouldn't want to go to a faster lens if it got bigger. What would be cool would be a set of compact short zooms between 24 and ~120 or so, for people who tend to see either short or long, like 24-50, 50-85, 85-120. I'd kill for a compact 50-85.