I don't have actual parses or anything to show to prove my points, but I have been doing some rigorous testing on the PTR with dual wielding. My gear leaves me at spell hit cap and about 21 Expertise. I use slow/slow weapons (Razorscale Talon MH and Grimhorn Crusher OH) and my gear is a mix of Naxx 25/Uld 10 gear. Sigil of Awareness is used, since I have yet to aquire SotVH yet. You may see more improvement with other builds if you do have SotVH.
Rune enchants: Fallen Crusader/Razorice
Fallen Crusader x2 works pretty well too, but FC/Cinderglacier does not work so well, since Cinderglacier hardly procs enough to be useful.
Blood Presence is more effective than Unholy Presence, even if using massive RP gain to spam Frost Strike (IT6 comes into mind)
I have done my testing without raid buffs on Patchwerk in Naxx 10. There were two tanks, two healers, and myself. I removed all buffs and only utilized Horn of Winter.
http://talent.mmo-champion.com/?deat...&version=10048
Rotation:
IT PS BS BS Ob FS dump
IT PS Ob Ob FS dump
Rime Procs can be used since diseases are running.
That rotation got me at about 3250 DPS.
IT PS BS BS Ob FS dump
Ob IT IT Ob FS dump
Rime procs can be used.
This rotation got me about 2800 DPS.
http://talent.mmo-champion.com/?deat...&version=10048
Rotation:
IT PS BS BS Ob FS dump
Ob Ob Ob FS dump
Rime procs can NOT be used due to being too global intensive and diseases falling off.
This nailed me a whopping 3784 DPS.
You can take one point out of Dark Conviction to put into Howling Blast if you'd like for that AoE utility, but you still can't use it for Rime procs on Single target DPS.
http://talent.mmo-champion.com/?deat...&version=10048
Rotation:
IT PS BS BS Ob FS dump
Ob Ob Ob FS dump
Rime procs can NOT be used due to being too global intensive and diseases falling off.
3320 DPS.
IT PS BS BS Ob FS dump
Ob IT IT Ob FS dump
Rime procs can be used.
3100 DPS.
The extra damage from Necrosis is almost useless when it comes to damage done and a DPS boost. While attcking patchwerk for 5 minutes striaght, Necrosis only did a total damage of 1670 with a +/- of about 50. That's not even that much of a noticable increase. Granted, having more hit will make it cause more damage, but it's still almost negliable.
The three points in Subversion can be switched to Blood Caked Blade, which will provide a bit more extra damage in the white hit department, but once again, that relies on how much hit you have.
These are all the tests I did with these builds. Your DPS may be different depending on how you're geared, obviously. Sigil of the Bengeful Heart will more than likely benefit the rotations using more Frost Strike than Obliterate. You may have more Hit/Exp rating to utilize more white damage bonuses. Regardless, I hope this helps any.