I know it varies by class and spec, but I couldn’t find any details on whether the S2 2p is worth breaking S1 4p over for any of ours. I tried looking into Ravenholdt, not entirely helpful either.
So, anyone know what the verdict is? Just waiting on full 4p?
keep it stabby, 
Replace it as soon as u have S2 2p.
In my case, the item level difference was enough to go with 2pc + 2pc
I have a s2 3rd piece ready for when I get the 4th.
Also, you run a sim to what it suggests.
2p/2p is nice. Get it as soon as. :3
Go back to Ravenholdt and type !fuu
Then check the spreadsheet.
Wasn’t worth replacing for me until I got a full 4 set, since I was gear capped last season. Mileage will vary based on S1 gear score and stat weights vs the ilvl and stats on the replacement pieces. Always best to sim that stuff when you get to the point of replacing, but our 2 piece is pretty underwhelming. Someone did the numbers on WoWHead, and the 2 set wasn’t an outstanding increase, and might be a loss depending on the stat trade on the pieces and such.
Our 4 set is huge, almost a full 9% increase overall, but the 2 set is mostly a primer for the 4 set. A lot of the damage comes from maintaining the 10 stack overcap for a long period with chaining Crackshot windows.
Pretty nice upgrade for me, though tbf it did mean replacing an old 626 piece…