Life Leech + Ghost Reaver viable?

Hi guys, short question:

I'm thinking about using Life Leech + Ghost Reaver on my witch.

But since the only way to leech life with spell damage is to use the Life Leech Gem, and that gem only leeches a very small percentage of the damage done, I think that spending skill points on Ghost Reaver and using the LL gem migh not be worth it.

Has anyone ever tested it? Is LL + Ghost Reaver good or would it be better to spend the passive skill points elsewhere and use a differet support gem (e.g. + Chaos Damage) than Life Leech?

Life leech is pretty much mandatory for most spellcasters that aren't a summoner or dual totem user.
Ghost Reaver is taken once you spec into Chaos Inoculation (which isn't recommended to do before act2 merciless and with less than 2500 Energy Shield)

The es recover from life leech is very huge. Sometimes up to 20%(maximun leech rate) of my current es in is 7k: 1400 es per second. that why i need vaal pact