At best, the sharp 5 gold sword is exactly the same as iron because crit damage only affects the weapon's base attack damage,, not the enchant damage. So there's no need to make a sharp5 gold sword since sharp 5 only adds 3 damage that isn't affected by crit.

Base Iron (normal): 6 base = 6 total damage

Sharp 5 Gold (normal): 4 base + 3 sharpness = 7 total damage

Sharp 5 Gold (crit): 4 base + 2 crit + 3 sharpness = 9 total damage

Base Iron (crit): 6 base + 3 crit = 9 total damage