I guess about average, slightly above on legs slightly below on hilts. I rerolled anything but legs hilts effigies and onyxes or something (I don't even remember the drops anymore) so I'll say about average on pet too.
It's something between 500 and 1k. I doubt it's fixed since gambling depends on enrage gained and being 'twice the chance' implies the first roll does as well. Regardless, each gamble counts as 3 attempts since you have one at normal chance and one at doubled chance. If just half my kc was gambled that's two times my kc in 1/900-1k (I never waited on araxxi) rolls. Nowhere near complain worthy as others but still unlucky.
Hi