For what it is worth, I tested using my mages to AoE SM to grind my warlocks in a raid. Each mob gives about 14 exp (-14 raid penalty). But.... I can AoE clear dozens in seconds.

So... I get about 2% exp per clear of Cath and another 1.5% for Armory on my locks. Takes a few minutes, rinse and repeat.

Not too bad actually - repetitive but faster than questing or soloing!

May not be variable unless you have a spare level 60 mage / priest team and 10 computers though

Edit: This method *works* but winds up being about 5000 kills per level. Which is slower than powering through on my own.