I wouldn't suggest going for the F5. Too many incompatibilities with older lenses (the F4 offers 99% compatibility).

However as pointed out the AF, being first generation, is too slow by todays standards (that however never stopped me from doing some sports photography) and you need to get used to it. If you use manual focus then the focus confirmation light (green light in the viewfinder) is a good tool to help you when in doubt about proper focus.