How good is the 4set for sub, i have it but i also have mythic gloves with mastery and multi in bag as well as the legs from blackhand with socket, is it worth dropping back down to two set to accompany them?
Sim it and find out.
You should sim it but I don't think dropping the 4set is worth it.
I replaced my 685 tier helm and chest for 700 multi/mastery helm and 706 multi/mastery chest for a dps increase. Best way to find out is to sim your gear.
Shadowcraft is a good rogue sim. Both sub set bonuses are probably stronger than you think.