Death Sipon mastery scale (MOP)

[Lúb]

Hello, was looking at some of the new MOP talents, and was wondering how much dmg / healing the new ability Death Siphon actually will do.
Anyone with beta and a mastery stacked dk (at 80 pref) to do some testing?
If it scales as good as everything else, I think we are looking at a rly nice spell for unholy / frost hehe

 

[Splosion]

Is it shadowfrost damage? Or just shadow. Unholy's coefficients for mastery are fairly low, but this could certainly bump it up above crit, just like having smourne/gurthalak does.