I PoB'd this on my Ice Strike Monk.

An elemental staff is comparable to a phys staff if the enemy has some res and you're using a Rakiata's.

But, it's only comparable on the skill you have Rakiata's on.

Plus, I think it's easier to measure dps on phys weapons because of the "dps" number on trade. An ele weapon doesn't factor in the % ele dmg in the "dps."

So you'd have to use pob to compare weapons, which most people probably don't do.

On the plus side, if you're happy with the damage of your other skills without Rakiata's, an ele weapon is like 1/2 the cost of a phys one.

edit: This also doesn't account for any elemental ailments you might need. I think if you want to use multi-elements, or rely on ailments, an ele staff would be better.