Good guide man!
Just a little opinion here. Desolation really doesn't seem worth it.
I personally prefer Wither with 4 dots and Flaming skull with 5 dots. They do insane damage, and don't hurt me
The way I look at it is, if I'm fighting something that I need to kill quick, it means it's something that is hurting me. In which case I don't want to be hurting myself. On the other hand if I'm fighting something that can't hurt me do I really need to take it out ASAP... In which case Flaming Skull does nicely.
PS. I'm 25 Staff, with 5 points in Spirit Mastery as well.