For years I heard the rule was 2F for calibers .50 and above, 3F for smaller bores. These days many folks use 3F in everything, but reduce the load; i.e. instead of 70 gr 2F shoot 60 gr of 3F, and get pretty much the same muzzle velocity (although perhaps a sharper recoil). The tables you see are usually titled "Preferred Loads" or "Recommended Loads", so they're not absolute. Just be aware that if you go beyond the recommendation, exercise caution and be alert for any signs you're overstressing things.
The situation was summarized nicely in a movie a few years ago:
"And thirdly, the code is more what you'd call "guidelines" than actual rules. Welcome aboard the Black Pearl." YAaargh.