Here's my take on the subject:
I run with legacy nats and I can tell you that provided you indeed have the old set, you don't need either preparation, or night stalker. Instead of preparation, I opted for Fan of Knives with increased radius rune. Most fun skill for DH in my oppinion, it just feels right when you're in the middle of a huge melee and you pop that Fan of Knives and everything in a 20 yard radius is gone. The damage output on it is simply phenomenal and it comes in quite handy especially against elites and rares which are a bit more mobile and manage to evade your bombs from the desolation rune on strafe. Instead of night stalker best two options are Archery for that extra 50% CD, or Perfectionist if you are lacking some defensive stats (which is most often the case when equipped with 4 pieces Legacy Nats)
Anyway, with my measly 72k dps, 25k life ~350 AR, 4k armor and only hellfire ring on my char and my follower (no room because of nats ring, or gold for that matter, for a leoric's...) I make about 900k exp per minute on average
Oh and one more thing... If you see an Empowering shrine, that thing is the shit! 5 sec cooldown on Fan of Knives, endless Vault and Shadow Power. Mobility meets immortality and devastation!
Great guide, excellent build to stick it to those boring and unoriginal WW barbs, who previously thought of themselves as the most efficient char/build for paragon farming.
I agree with removing preparation, but removing Night Stalker without the extra 20 Disc from New Nat's is questionable. You'd have to be really good at managing your Disc.