The F5 is quite a bit bigger and heavier than the F6, as others have noted. Whether that matters or not is up to you. In general the F5 is a better choice for longer, heavier lenses. It balances them nicely. The F5 is also a lot cheaper than an F6.

For my money, the best cameras ever made are the Minolta Maxxum 9, the Nikon F6, and the Canon EOS 1-V, in that order. The F6 will run you around $1000 used, while either of the others can be had for $400 or less. The F6 is far and away the best film camera Nikon ever made.