Just what extra speed do you want with focussing? The F4 is as good as AF can be from the era it was made and will still outsmart and outpace your personal reflex action all the time, everytime. Why waste money on an F5 which is one of Nikon's obese monstrosities, whilst a gem with technology it has long been acclaimed as to heavy to carry comfortably. (my opinion also). The metering is almost perfect especially with flash, really it seems a no-brainer to me.
I have used an F4 over many years, but that too got to heavy to lug around when walking, so splashed out and bought a used F6 which is much more comfortable to use.
I am not going to argue that the F5 is not heavy. Even with Lithium batteries, it will be on the heavy side. It will not be as heavy as the D4 or D5, for example, but I have a good, comfortable bag to lug it and a lens or two around in so I will be okay. I am also not going to argue that the F4 is not a great camera. It is. It is a phenomenal camera. My problem with its AF is being able to keep up with odd angles. I have been undertaking a personal project lately, and that has been photographing downhill mountain biking using film. I am a big rider and watching DH racing is a ton of fun. It is awe inducing on both a human and technological scale. Where the F4 is struggling to keep up is the ability maintain focus at odd angles. A downhill track goes up and down and swoops in different directions. Then, there is the rider who takes different lines on the same bit of track creating more randomness. The F4 simply cannot maintain focus fast enough. It cannot rotate the lens fast enough.
Example: lines up but rear wheel hit a rock and stepped out leaving just the front number plate relatively in focus. The focus point was on the body:
Another. Panning with the subject going further away towards the end of the pan. Plenty of contrast and light there. It was trying but it just could not keep up. In the end, only his bum is in focus. Yes, the negative is dirty. I know this.
I have a Gitzo Adventury. When I head out to a race, I regularly carry the F4, the D610, 80-200/ 2.8 D, 18-35D, 50/ 1.4D, 60/ 2.8 macro, film, and a few other things like water and a jacket. Adding a pound really will not harm me. I also regularly carry my Bronica ETR/ ETRSI and about 5 different lenses and a couple backs at times when I am out hiking to do landscape stuff. That bag is really quite comfortable, and balances very nicely the weight inside.
I should also add that the F5 will not be my 'walk around' camera. It is a camera with a purpose. Shooting biking. My walk around 35mm is, and always will be, my Pentax MX.