Mmm, maybe I just need to sleep more than 2-3 hours in 2-3 days, but:
So, taking my stats - 2018 crit raiting (+3,36%) which makes 1% crit = ~600 raiting
and mastery - 5304 raiting (+22,1%) => 1% mastery = 240 raiting
For example,
Tay'ak
Firstly, at this moment mastery doesn't affects any of our pets, so damage of deathknight without his pets is 4,87/6,18=~78,802%
And shadow damage of dk without pets is 53,6%, so it is 0,536*0,78802=42,237872%
So mastery affects 42,237872% of our damage (I don't think that Tay'ak in HC is specific encounter, but imho it is the closest fight to patchwerk this content)
So, 1% of crit bumps up our dps by 1%, so you need 1/0,42237872=~2,3675435% of mastery to up your dps by 1%
And 1% mastery is 240 raiting, so 2,3675435*240=~568 raiting.
568 mastery or 600 crit for 1% dps. Of course here can be many mistakes, so I don't really sure >_>