I am currently looking for a way to sim the exact output the tier13 4piece bonus provides in BiS gear.
What I'm doing atm and seems to be working somewhat fine is just change this line:
head=hood_of_the_faceless_shroud,heroic=1,type=cloth,ilevel=410,quality=epic,stats=1336armor_489int_824sta_370haste_280crit,reforge=crit_hit,gems=burning_shadowspirit_50int_30int,enchant=60int_35crit
Or any other line featuring a setpiece. I just change the name of the item name and it seems to sim only the set bonus because the stats still make it through. From what I can tell the 4piece provides about 1400ish DPS and seems somewhat plausible, the only thing I'm wondering, is there anything I've missed by doing it this way?