Rogue Killing spree In depth question

I've been messing with killing spree custom specs to maximize the damage.
Got a couple of questions.
First, regarding ONLY killing spree for burst, NOT sustained DPS, it should be more beneficial to get 2x slow hard hitting weapons correct?
2nd, Im coating both my weapons with Instant poison, because Killing spree applies poisons during the ability. Here's where the hardest question comes into play. What would give me more damage during the spree? Vile poisons or Improved poisons? I can't seem to find anything about this topic and if anyone has an idea would be highly appreciated.
P.S If you're lazy, Vile poison - 20% increased poison dmg
Improved poison - 50% increased frequency of applying instant poison

1. Dual Havocs call (slow wep) is best for maxing KS

If you're asking about this for pvp purposes, this is the spec you want - http://armory.warmane.com/character/...ecrown/talents He uses dual havocs for the same reason you ask about it.