Well, 2pc shouldn't be hard to figure out for patchwerk fights (on movement heavy fights it will be used more now that its an alternative to DP while moving) - you just take your current Death % of total damage and times by 1.55 and you have a pretty predictable amount of damage done coming off the 2pc bonus.
For the 4pc bonus it isn't that difficult either - just assume 100% chance of 3 orbs on MB, 100% uptime on shadow empowerment, and subtract the dps of your current orb procs and your current uptime on shadow empowerment (since that is overlap with your existing dps).
Generally the conclusion will be this though:
2pc will be pretty fantastic, I might even wear it in pvp if I can get away with it and DTR and an int trinket and still pull off enough resilience to not be globalled.
4pc will suck, so badly that they will nerf tier 12 4pc so we don't keep wearing tier 12 when we have access to tier 13 just because the PP value in the set bonuses are so bad.... oh wait they already did this ^^