they really are 2 different IEMS. whatever the frequency response graph may tell, details are different, imaging is different, the f111 sounds almost smooth and warm if you ABx it to the er4.
the first thing I though when listening to the F111 was "omg it has nothing to do with an er4, those guys @ headfi are all on crack!"
in the end it comes down to what oneself is looking for:
3D sound, less fatiguing, no harshness, more and rounder bass= F111
more of a super wide axis of instruments, surgical separation, control and damping over 9000, sending reverb in the myth section, all the sounds even the nasty ones=er4
to me er4 is a monitor, the F111 is an enjoyable IEM that happens to have a pretty even sound signature ^_^ . saying who's best is a hard job.