I decided to use Nibelung over the chieftains staff last night in 10m icc to see how the changes worked. Overall it did better than before when it proced. a couple times the proc uptime seemed to be about 75% (or more) others less than 10%. they survive the AOE much better now so up time is longer. i noticed dmg between 1.2k and 1.7k per hit pending resists and it almost never missed. i didn't look at the recount close nuff to give specific numbers on dps.
my personal performance dropped a little due to the lost stats and atleast twice i was close to running out of mana when shadow fiend came off CD so was manageable but not something i'm used too.
its not a bad staff but i will be using chieftains most of the time unless i'm bored and want to see the pretty little things.