I'm almost certain that the 4pc will give more dps than 2 warforged pieces would give. 4 pieces of our T16 have all red sockets in them (with agi bonus), and considering agility is so good for us I don't think you can make up for the lost dps from missing out on 4pc with 2 more warforged pieces.
I quickly checked what the stat gain would be when taking off-pieces for legs and shoulders: +76 agility and + 694 secondary stats (cause of less red gems it's more secondary than agi).
According to some very quick calculations I did 4pc would give around 4300 dps, while the stat gain with warforged gear would only give around 1850 dps.
This is all just very quick math so don't assume this is very accurate, but until proven wrong I know I will go for the 4pc