You know, Scene, that's actually a really good idea. Be right back, Lightning Bolt spam on the way.

I'm not quite seeing how you draw the conclusion that Necrosis is better than desecration in a movement heavy fight. The second i get back to a mob in a movement heavy fight, desecration is reapplied (either through SS or PS).

When you are out of range to use desecration, you're also out of range to use necrosis. So i fail to see how that works in that case.
I can somewhat see the point if you have to move around in melee range, but desecration radius is often big enough to circumvent this.

Also there are only a handful of fights where you get targeted and attacked by a boss, and in most of those cases it's with enough intervals so you can reapply BS.

Just break it up for a second.

You trade 2 points in Crypt Fever and 3 points in Ebon Plaguebringer for 5 points in Dark Conviction.

Dark Conviction is about 0.55% dps per point (stated several times before in this thread).

My diseases are about 15% of my dps. Increasing that by 10% is 1.5% dps per point.
2 points in crypt fever is already better than 5 points in Dark Conviction.

On top of that you have Ebon Plaguebringer, 13% more magic damage on nearly all your attacks is just too good to pass up. Probably around 8% dps for 3 points.
Sure a warlock or druid can provide this, but none of them can do it as well as a DK does, since ours is easy to spread in aoe. And the warlock one costs the warlock dps (he could have used another curse)

So basically you put those 5 points back in unholy and VOILA. You're right back at the default build that we started with.

The only thing you're trying to discuss is saying that blood > frost as offspec tree. Which is debatable.

Butchery / Subversion / Imp IT and RPM are all faily weak talents. The real battle is between 10% shadow/frost damage vs 4% 2H damage + 400 AP

The AP component is faily static. While in naxx that provided about 10% more AP, in ulduar thats already down to about 6.5% extra AP.

The 4% extra damage applies to white dps, all strikes. BCB.
The 10% extra shadow/frost applies to diseases, scourge strike, DC, UB, Icy Touch

In the end they're likely to be near equal components. Lets for the ease say they both effect about 60% of our total damage. (This is random number, but it puts things in perspective) In which case Black ice boosts dps by 6%, and 2H spec boosts dps by 2.4%.

Blood might be better at the beginning where 400 AP might be better than the 3.6% dps boost that Black Ice provides over 2H spec.
But eventually Black Ice will outscale this.

I'm personally using a blood subspec at the moment. But eventually ill switch to frost.

Corruption is good to use if you have the 2pT7-bonus. After that, I honestly don't know.

I think that a macro like this will work as well

/cast [target=player] Sacred Shield

(or I should say, it does work, assuming I've remembered it correctly).