Looking at your current progress, you should use the Tier Legs, since 4set is so incredibly OP.
When u progress some more, go with HC Legs and HC Offset Helm from Rhyolith, until you can get Rag. When you get Rag HC, you can either go with the 397 Ragnaros Offset Gloves, or the 391 Offset Alysrazor Legs (Gloves setup gives a minor Int and Mastery gain, Legs setup gives a major Haste and Spirit gain, it comes down to what you prefer, but I would go with the Legs.)
Off-topic, but you should go for the socket bonus in your Shoulders (replace 40 Int with 20 Int/20 Haste), and ignore the socket bonuses in your Gloves and Belt (replace the 2x 20 Int/20 Spirit gems with 2x 40 Int). Also get 65 Mastery on Gloves. If you can, replace Fiery Quintessence with... something... Necro or HC TM.
But yeah, 4set is a must
By MY hand, your slack shall be extinguished, eternally banished from this realm.