Double Experience for each level 60.

[Shurrikhan]

I've no issue with seeing up to 50% faster leveling, essentially a couple dungeons (or a leveling and trial roulette) and a few FATEs per level, but I don't see it as being necessary either. I do however dislike the benchmark you've chosen for it. At present, we get tremendous bonus experience on all but our highest level job. There's no arbitrary check of having one, let alone two level 60s, which could otherwise push us to leveling to 60 a job we don't necessarily want to finish at the moment. Placing it at exactly 60 encourages people to rush for 2 60s immediately, regardless of what they'd actually want to level, and then gives no further bonuses after that point. I'd rather see something that continuously adds on to the bonus, but in a de-exponential fashion or similar.

For instance: Armory bonus: Increases experience gains from combat and non-quest rewards by 50+(1-log<all levels of classes/jobs above your equipped level>)%.

e.g.
Level 30 - with a level 40, 60, 60, 60, 36, and 33 = additional 104% exp., or +154% exp rate total, +204% when rested. (Only a 54% increase over current when you consider that there's no longer an additional 50% bonus when under level 50.)
Level 50 - with 3 60s = additional 48% exp, or a total of +98% exp rate.
Level 50 - with 2 60s = additional 30% exp, or +80% total
Level 50 - with 1 60, nothing else above 50 = 0% additional exp, or +50% total
Level 50 - with a 52, 54, and 60 = additional 20% exp
etc. etc.

Speed you through the worst levels, and adds tapering gains with each class/job leveled in the category.

Note that the most this could ever get to even with, say, 9 60s is a 95% bonus at level 50, 90% at 51, 86% at 52, 79% at 53, 73% at 54, 65% at 55, 55% at 56, 43% at 57, 26% at 58, and 0% at 59.

(This math is not even of spit-balled quality. However, it does demonstrate what I'd go for with a system like this.)