Double Experience for each level 60.

[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.