As someone who is using the F100, F5 and F6 I want to add some information:
I will have to disagree.
The F100 cannot be recommended as a reliable camera due to the weak back door alone. It is a very well documented problem. Getting a replacement might have been easy some years ago, but today it is neither easy nor cheap. However, it is more than enough if you want to treat it as a redundant body that you do not care to rely on.
+1.
One friend of mine bought a used F100 in 2005, and it had cracks in the plastic clams of the back door. He had to replace the backdoor, which wasn't a problem at that time because spare parts were easily obtainable.
Another friend had broken plastic clamps last year. And he has difficulties fo find the spare part now.
These plastic clamps are indeed the weak point of the F100 (and the F80, F75 too). Most photographers close the back door by pressing it to the camera body. That causes lots of pressure and stress onto the plastic clamps. Over the time then cracks happen because of this, and finally it breaks.
F90(X), F5 and F6 have very robust metal clamps which don't make any problems.
With my F100 and F80 I use the following technique to avoid broken plastic clamps: I first put the switch on the body down, then carefully close the backdoor, and after that I put the switch on the camera body back in the closing position. By that technique I avoid any pressure and stress on the plastic clamps. Therefore my F100 and F80 are fine even after so many years of use.
I highly recommend that technique to all F100, F80, F75 users!!
If someone is looking for used F100 or F80, he/she should really have a detailed look at these plastic clamps: If there is only the tiniest crack you shouldn't buy it.
The F6 brings a whole lot more to the table. Perfect ergonomics, toughness, weather sealing, full customization of operation, new af module and meter... Matrix metering with manual focus glass is worth a lot on its own. It really is in another league.
Indeed, the F6 is really a league of its own and significantly better than the F100 in every aspect. In a side-by-side comparison you will find more than 25 parameters in which the F6 is surpassing the F100.
The F100 is a very good camera, nonetheless. Especially as it is currently extremely cheap on the used market (same is valid for the F5). But you definitely must have a look at its weak point, the plastic clamps.
Best regards,
Henning