You could go as far as Crated gear, pentamelded for every class on a character.
Now you can't perfectly pentameld for every class, Paladin wants something slightly different than a warrior. Even DRG and Reaper want something slightly different in skill speed.
So you can have, as a starting point, "perfect" gear, one set for each set of equipment. Scouting, Fending, ect. That's 620.
Not good enough?
Fine, wear that, do the current EX, get a lot of tokens and chests, and you can get 625 weapons on every class. Might not be better then perfectly pentamelded, but might be better then the wrong meldings on your off characters, this brings everybody back up to power level, assuming perfect play.
Next step? Well, the weekly limited tomestone gets you 620 gear, and then you could ride along with hunt trains to get the nuts to upgrade it to 630 gear. So the limitation here is 450 tomestones per week. This won't get you a full set. So lets assume you've got friends at the same unlimited power potential. So you run savage, and they give you the coffer from all four, that's four more pieces of 630. Call it two weeks to get one nearly perfect set. Again, you can't QUITE perfect a set for more then one class per type, so you'd have either a perfect paladin or a perfect warrior. So, to get all 7 to the top, we're talking the entire length expected between patches, about 4 months.
Next step? It's ultimate season. TOP performance jokes aside, in theory if you play perfectly, you could be on an ultimate team with that level of gear, and farm ultimate weapons for every job as well. Wont' be noticeably better then the weapon from the savage circle, but it'll be shiny, and typically while not enough better to be worth it, come on... eveybody wants it.