I haven't used the F90x but I've had an F80 for several years and love it.
The ergonomics work really well for me and the functions suit my needs down to the ground. If I were really picky then I'd like to see mirror-lockup and a bit more speed from the motorwind. Other than than I simply can't fault it. The metering in particular is excellent.
If you have manual Nikon lenses and want to keep using them then go for the F90x, unless you're a fan of separate metering. Otherwise I recommend the F80.
For more advice try www.nikonians.org
All the best,