I have both the F90X and the F100
In bright light the F90X finder is much better since info can be hard to read in the F100.
Approx 1/2 stop accuracy vs 1/3 stop accuracy doesn't make much difference, especially not when shooting B&W. Even with colorslides I have been more than happy with the result from my F90X. The Ergonomics wise the F100 shines and it baances better with large heavy lenses e.g. 85mm F/1.4 but I use both and if you don't need another camera stick with what youve got its plenty good enough.
Best regards