A 31/0/40 build, http://www.wowhead.com/?talent#IfxM0...E0hVrcubsV:Mrw
You'd have almost no downtime since:
a) You wouldn't require (much) healing due to Siphon Life and Soul Leech (even though it was just meant as a filler)
b) You get the Health from Siphon Life and Soul Leech for Life Tap and you have Dark Pact.
I'm talking about PvE, not-so-endgame, more like Naxxramas and Obsidan Sanctum.
So, would it work?