As far as i know +elemental damage on SoJ (and in every item anyway), applies only to the physical damage done by your weapon. There is a blue post that explains that.
If for example you have a weapon that has 100 physical damage and your SoJ adds 6% elemental damage, as fire for example, your weapon will do 100 physical damage + 6 damage as fire.
Elemental Damage affixe is override by the element of used skills. However, only Frozen damage is noticable if you don't use elemental skill like FoT/Thunderclap or Cyclone cause it can chill ennemies. Otherwise, it doesn't matter.
But it's really really good with black weapon cause it scale at his maximum potential.
SOJ is nice for higher mp(at least 7) and/or ubers. Just not worth for farming on lower mp
I have to disagree here; probably the best use for SoJ is mp0-1 tempest rush farming with +damage to sweeping winds and a good spirit regen. You can swap out with a good dps ring for when you cast sweeping winds initially.
I dunno man.... a decently rolled hellfire will get far higher dps imho... and your other ring is probably going to be Nats....
My Hellfire ring is not the best, but taking it off makes me lose 45k dps. Adding a stone of jordan (6% elemental dmg, 30 to elites and 5% sweeping winds is what I have) still give me more dps. My SoJ is actually 15% more dps compared to my decent hellfire ring (tested on Azmodan MP10 numerous times). Imagine what a better SoJ could do