Rule of thumb is Weapon Damage = x10 Main stat = 10x secondary stats. That said, it does vary by job and secondary stat. Dervy's blog above is a great tool for a few of the jobs and to give you a good idea of how it works. Just remember if you hold back on a weapon with 2 less WD because it has CRIT instead of Skill Speed, you are effectively losing out on the equivalent of 200 CRIT.