Double Experience for each level 60.

[UltimateAoe2]

I.... really wish people would stop adding that "assuming you have a 60" thing. On my main (C'alih), I have level 60 classes, and get 100% bonus to exp and Fates and such when below 50. On my alts, I don't have any 60 classes, and I still get 100% bonus when not on my highest class (and below level 50). Haven't taken a closer look on one of the alts that don't have any level 50s yet, but will try to remember to do so tomorrow.

As for levelling faster... Keep in mind that if you're in a dungeon where you're synched below 30, you once more get the benefit of the Brand New Ring if you equip it. If you're synched to below 25, and have a Friendship Circlet, you can equip it and get the bonus from it again.

Personally, I'd be alright with a slight increase in the bonus for each level 60 character. Say, 10% or 20% extra for each level 60 character.

I just say assuming you have a 60 since I dunno peeps. I just assume people have 1 60 then level the rest on their own time.
I know about the 50% buff from 50 if you have a job higher than the job you're leveling (IE: level 55 WHM and you're leveling a level 51 BRD)

It applies for 50 as well. You get a 50% bonus if you have a level 50 job while leveling any other job/class under 50.

[Canadane]

I just say assuming you have a 60 since I dunno peeps. I just assume people have 1 60 then level the rest on their own time.
I know about the 50% buff from 50 if you have a job higher than the job you're leveling (IE: level 55 WHM and you're leveling a level 51 BRD)

It applies for 50 as well. You get a 50% bonus if you have a level 50 job while leveling any other job/class under 50.

You actually do not require a level 60 or a level 50.
Just so as long as you're not the highest of your classes you'll get the full bonus.