affixes on items are usually additive, Talents are usually additive, but sometimes multiplicative. if it isn’t in the description, just check the Stat Page to see which way it goes. upgrades from Skills don’t apply towards the Cap, so you could have +350% Crit Dmg. and go even higher with Warrior (or any Class) by putting Skill Points into Earthshatter, which has a bonus for Crit Dmg when you put Skill Points into it.
Twister has a Taunt ability, and also stuns enemies caught by the Twister for a short time. so lots better to use Cool Down with it instead of Attack Speed. also, Twister lasts for 5 seconds while it moves away from the caster. Twister 40 with +60% CD lets you cast a Twister every 1.2 seconds. as long as you don’t have to get out of the way of an enemies attack, they get sucked into the Twister. enemies could be getting hit by multiple Twisters, because of the range of their AoE will overlap, depending where in the line of Twisters they are, they could be getting hit by 2 to 4 Twisters at the same time. if you have boosts to AoE, maybe get hit by all 5 Twistes!. with the Twisters buffed up this much, enemies are getting hit 5.6 times a second from each Twister, and you would have 5 Twisters being cast, moving away from you for 5 seconds, then the spell ends.
as far as using the Berserker Set for Stunning, as long as it works for your Build, stay with it. there are ways to improve a Stun Build to make it stronger. there is a Set bonus that increases Dmg of Stunned enemies, and one that increases dmg. when using high Attack Speed.