This is the reason I flash on the pull. If you are getting into position to use an unbuffed overpower without vengeance up you are gonna take a big spike in damage, likely freaking out the healer and making them think twice about DPSing. If you use vengeance then unbuffed overpower before unchained/zerk you are losing potency from vengeance by delaying zerk/unchained by 2 GCDs. As you reach the last pack, just HS 1 Unchained/veng > Maim 2 IR/Zerk > go to town. Even if there's 2 untagged mobs in the last pack the range on overpower will rip them back easily if they head for the healer.
You refresh the timer on the stacks as you are half way through pulling with a HS > Maim so the 5 stacks last more like 45 to 50 seconds. Same idea as OT unchained opener using infuriate > wait 29 sec > vengeance to refresh stacks > wait 15 sec > MT pulls > you get unchained + 2 inner beasts on opener before turning defiance off.
Indeed! It's slightly less effective as you lose 6% crit rate from 3 stacks (maim, veng and zerk). It's useful if you are splitting the pull between bosses into 2 or in a gated dungeon, otherwise I prefer to pull everything and burn those on the bosses so I can keep defiance off for them.
I unchained before maim so I gain an extra 2% crit from the additional wrath stack. As unchained wears off, I infuriate then SC so I lose no potency.
I wouldn't use zerk while approaching before steel cyclone. You'll have to wait for the mobs at the back of the pack to catch up and get into range to hit them with SC, that's a lot of healing and damage lost if you don't wait and if you do wait, you'll miss the 9th hit on zerk.
For pure DPS I'd do things differently like moving vengeance to after the first overpower so all hits are fully buffed, but for max survival, you should always get bloodbath/veng up before the first overpower. It slows incoming damage down to a crawl and gives the healer confidence to go ham.