According to the spell description, Ray of Frost deals 215% weapon damage and disintegrate deals 155% weapon damage. However, if I enable the damage numbers in the option menu I can see that I deal more damage using Disintegrate (besides, enemies DO die faster). I've tried it with a few monster types on Act 3, and it's unlikely that all types were resistant to cold. While this makes sense (Disintegrate is a higher tier skill after all) I don't understand why the spell description says the contrary. The only thing that comes to mind is that Disintegrate is somehow "faster" and hits more times.
So why is Disintegrate doing more damage?