Never owned an F5, but had plenty of F4s cameras. Built to last, that's for sure, but not the best ergonomics in my view. Still, if you want heavy and solid, there you are. I'm sure the F5 would be as good or better, and newer too.
After a while I got real tired of toting those big cameras around. I'm not a commercial photographer, and have no need of cameras designed to go through a war. A medium format camera is no bigger or heavier than the F4s! My N80 was a little gem w/ one of the quietest shutters in photography, but that dim, small VF didn't work for me. My go-to Nikon has always been an N8008s. Fantastic viewfinder/metering/ etc, takes cheap batteries, and you can buy them for $20 or less now. Better than an F100 in my view. The mirror slap of those turned me right off, although the build quality was great.