revenants and animates.
Revs while lacking in many ways do need alot more skill to cast reliably(115?). Animates are more powerful when you have higher necro skill. For animates the skill must be real skill and not item skill bonus. I have a 99 necro and when I animate a high famed corpse I get a lich, when i put on skill+ items I still get the lich. When i use my real gm necro I get the skely dragon.
Back to OP Wither is spirit speak based for damage. @ 120 SS you will be at max damage for wither saving for SDI. Slayer books dont effect necro spells even though it looks that way some times. Most mobs have very low cold resist.
Now even for a mage vamp form isnt a bad idea(garlic) for the mana regn and mounted ability(garlic). 120 skill helps here as well!(garlic). IMO its better than lich because of being able to mount.(garlic)