How long should we keep t11 4 set?

[:1]At the moment, I have the t11 four set but also 2 pieces of t12... should i remain with the 4 set untill i replace the other 2 pieces?
the t11 4p isn't THAT good, go w/ the t12
Sim it. Check the reforgings at wowreforge.com, and then sim your current, and then compare it to the properly reforged T12 2-set using Femaledwarf.

Since you're in full 359 T11, I would imagine T12 2-set would be an upgrade, especially if you can replace the other two pieces with off-tier Firelands pieces (T11 2pc is abysmal).