Actually, believe it or not you want Slow/Fast as mutilate. The only time you want Slow/Slow is if you are pvping and hope to wipe someone out in the first couple of stun sequences. So stick with mutilate, although it just got nerfed.

edit: from EJ forums
PvE Mutilate, fast and flawed advice
Highest DPS dagger mainhand, have at least one fast dagger in either hand.
Fastest dagger - Deadly Poison, Other dagger - Instant Poison.

Priority:
* Ensure that there is a bleed (ie. Rupture, Deep Wounds, Rend) on the target.
* Start up Hunger for Blood.
* Start up Slice and Dice however you please, really.
* Use vanish whenever possible for Overkill buff.

1. Keep HFB up.
2. Keep SnD up (mainly via Envenom).
3. 4+ combo point Envenom.
4. ToT when off cooldown, especially with 2pc T10.