Aw yeah, Ren has over 500 AAs. Still a long way to go, not just in AAs but also in levels... but at least I've gotten nearly all of the fundamentals out of the way. He's gettin' pretty tough now.
And yeah, sure enough, I saw Ren's AA exp slow down once I crossed the 500 mark. So what I've heard is more than likely true -- AAs slow down at every 500 points.
As for Cybel, she's a couple hundred behind, but slowly catching up. I've been burning Lesson of the Devoted with both of them grouped together... seriously, the AAs fly when they're working together. However, I've been running regular groups with Cybel alone.
Once they have all the fundamentals I believe they'll need, I'll bump both of them up to level 70 and work on the next set of AAs there. Origin, especially, is something I'll want... think "Hearthstone." Yarr.