For example may weapon ako na meron affix na +1000-2000 fire damage, nagbebenefit ba ito sa +20% fire skill damage?
Bro from what I know (please correct na lang mga chief kung mali)
1. If you have a weapon with elemental minX-maxX damage, you should only care about re-rolling the min-max dmg stats as high as possible REGARDLESS of the elemental damage type. Why? Please read #2
2. Your RUNE SKILL will always dictate the elemental damage type of your weapon. For example, a DH Multishot Arsenal Rune is a fire damage, and if your weapon has elemental min-max COLD damage, your weapon elemental dmg turns into FIRE because of the rune skill. Basically the % fire skill damage procs the MS Arsenal Rune skill, then MS Arsenal damage is based on weapon damage (white damage + elemental damage combined) = higher DPS. I don't know how to explain it better but that's how it correlates.
3. An exception to #1 and #2 is if your are using %physical skill damage. Since physical skill damage has no elemental damage, whatever is elemental damage type of your weapon becomes your elemental damage.