Approx 1/2 stop accuracy vs 1/3 stop accuracy
I'm not sure what you mean here, but the F90X does have 1/3 stop adjustment to the shutter speed, exposure compensation is in 1/3 and even the Program shift is in 1/3. The exposure graphic on the viewfinder only shows 1 stop either way, but in 1/3. BTW, exposure compensation is up to +- 5 stops!

To the OP
The question you have to ask is: are you happy with your 2 F90X?
I am more than happy with my F90X. So much so, that I bough 4 of them! All are in excellent working condition and no "sticky rubber" or peeling backs!. BTW, the F100 suffers a bit from the same, but it is different: the rubber becomes sticky in some, but never heard of it peeling away. The same goes for the F80.
Here in the UK, I didn't pay more than 45 for any of mine, while a F100 in good condition on sale with a reputable seller goes for 140-160.

This is the way I normally use my cameras:
Camera in Aperture Priority mode. I use my left hand to cradle the lens from bellow and the thumb and index fingers to zoom/focus. To change aperture is with the thumb and middle or the ring finger. My right hand has a firm grip on the camera with the index finger hovering the shutter button, ready to fire or to move across to the exposure compensation button. The thumb is free to move to the command dial to change values for the exposure compensation.

I don't have a F100, but I do have the F80 with the same "modus operandi" as the F100.
I found awkward to have the index finder of the right hand to change apertures and then move it up to the shutter button. It isn't as quick as it is operating an aperture ring on the F90X.

One thing the F100 has is the Custom Functions are integrated on the body and are about the same as the ones for the F90X available via a PC software. That is the one accessory I haven't: I'm missing the specific cable to connect the F90X to a PC. The software is now freely available: it is the Softalk 2000, usable with any F90 series, F100 and F5, here: http://www.cocoon-creations.com/COCO...Features.shtml. I would love to have the Easy Exposure Compensation in A mode, but need that cable.
Have a good shooting!