Nostalrius Begins - Quality wow vanilla realm (1.12)

1. Rend doesn't seem to be affected by any stat.
2. Overpower does not trigger from a dodged special attack.

Dodge does trigger Overpower, but it will show in combat text only if you have enough rage. I'm talking from my experience though.

Rend should only be affected by AP + weapon damage/speed.
See: http://vanilla-wow.wikia.com/wiki/Rend

Yes it seems it only happens bellow 5 rage.
I know which stats should benefit rend, I'm saying they don't, been trying with different weapons and buffs.