Not mentioned so far is Lens compatiblity.
With the F80 you loose lightmetering with non AF lenses i.e. AIS and AI.
F100 is compatible with non AF- as well as G-lenses
F90X is not compatible with G-lenses, at least not in M and A modes.
I use 28mm AIS and 180mm AIS on my F90X and the only drawback is I have centerweighed and spot metering only but since I use spot 95% anyway its no problem.
How does the viewfinder compare ?
Do you like your camera light or a bit more heavy (rare, medium or welldone :) )