An F5 will never be an F6 IMO ... if you have your heart set on an F6 and can afford the extra don't consider the F5 because you'll always wonder what you missed out on even if the differences are minor.
I tend not to use auto focus on my F6 or D700 because they both have such good finders for AF cameras but on the odd occasions I have used AF the F6 seems a little faster and more positive to me. I wish my D700 felt as good in the hands as it's film counterpart ... it feels quite unwieldy in comparison for some reason. Better weight distribution and a slightly longer thinner body make the F6 handle completely differently!