The only one that matters are Tiaras, with their stunning +15% dbl +15% trpl. Because that might not hit home just how stunning that is, it takes you average attacks per turn from 1.14 to 1.59. So that's a ~40% increase in your auto-attack damage, not to mention that it lowers your average turns per full burst from 8.77 to 6.29. Of course, +burst and damage taken will realistically accelerate those numbers.
Oh, and the runner-up set bonus are necklaces, which give 10% chance for 35% Crits. So that's nifty when it procs, but you'll still want Tiaras.
I don't understand what you mean "14 days each to SSR", but hey, you do you, I guess.