Best weapons for Mages are Mythics...period... BLM mythic at lv99 has something like... MAB+50. How I know this is it goes +5-10 MAB every 5 levels.

That do crazy... amount damage. Could do something like 15k-40k dmg a tier5 with brew on. It pretty muh gives you extra 5-10k DMG to your high lvl spells.