I've crit just over 100k in arenas... as a resto druid.
4. 236k (with 67% res at the time! no berserker myself and not temple-BG)
6. Starsurge (prob. instant as well)
Crits in temple of kotmogu are kinda useless. Did a 9 million powershot (pre nerf) once on a green geared shaman :P
2. 728k (with rune of re-origination proccing and me and the enemy had orbs a while with berserker)
3. Chaos bolt (also with 2 raid trinkets but in arena -_-)