4.15 is more damage even with a bad calamity or even nats slayer. You would have to try it out with the gear you have on hand to know if its for you or not.
I am not sure which I enjoy more, 4.15 or 2.84 but its nice to be able to pick from either.
Im at 4.18 (50 paragon ias) if i equip a 1h with 7% attk speed if you wanna look at the gear needed (2.88 with the 2h, its nice to be able to swap and keep both max breakpoints)..
You need 7% on all slots (including tnts, makes it very hard since you need 48+ on them too) unless you wear an ias neck or the gem. 48% tnts are the bare req (like riff said) as well as 7% ias on bracers to reach the final break pt.
Keep in mind at 35+ shooting yourself requires smoke screen. Its hard to use the gem unless your going light ball.
You don't need 7% on every slot. It helps and its very bad if you don't have it. It's funny to me how often people come in and say "You must have X on Y pieces of gear" and are just flat wrong. Should take a hint from RiffSphere and do the math and then tell people what IAS from items/paragon is required.
I am not sure which I enjoy more, 4.15 or 2.84 but its nice to be able to pick from either.