I'm doing these tests for my own benefit to figure out what lenses to take with me in a future trip but I thought I should share my conclusions with you.
I'm not going to attach the photos unless somebody asks for a specific shot, too much time to put them together.
Testing conditions: flat chart at about 1.5-2 m away (too cold and too lazy to do the longer distance yet), shot at "landscape" apertures: 5.6, 8, 11, 16. Sharpened as per my routine (F16 got more).
@ 24 mm
24 F1.8 _ 24-120 F4 _ 18-35 F3.5-4.5
24 vs 24-120
Center: while the 24 has at times a small advantage for practical purposes they are very close at all apertures (again: 5.6-8-11-16)
Corners: there is no comparison, the 24 is by far better at all apertures. The sad part is that the 24-120 barely improves in corners with decreasing the apertures, even at F16
24 vs 18-35
Center: the 24 is a better at F5.6, otherwise they are very close
Corners: the 24 is much better at 5.6, and from there the difference is decreasing: better at F8, a little better at F11 and only a little better in extreme corners at F16
24-120 vs 18-35
Center: very similar, give or take
Corners: the 24-120 is worse at F5.6 (with a little better contrast though) and from there the difference is even bigger in favor of 18-35.
@ 35mm
18-35 vs 24-120
Center: they are very close
Corners: the 18-35 is a little worse at F5.6 and F8, even worse at F11 but a touch better at F16
@ 50mm
24-120 F4 vs 50 F1.8G
Center: the 50 is a little better at all apertures
Corners: I was surprised to see that my copy of 50 is definitely worse in corners at F5.6, a little worse at F8, about the same at F11 and a little better at F16
Next will be from 70 to 200/300 in various combinations of lenses