personally, I am happy to stick with my 24-120 F4 it is a superb lens and well worth the extra cost for fixed aperture across whole range, super sharp wide open and IS that equates to about 3 stops.
I am so happy with the IQ from this lens that it has now become my prime and relegated both the 24mm f2.8 & 50mm f1.4 to the cupboard and I never thought it would do that as I have always been a prime lens person.
How times and performance changes!