Rip & Tear Mk XV
 Zealot Build - Warhammer 40k: Darktide 

Ranged Weapon is mostly about preferences, I like the Zarona's fast 1 tap potential on gunners & specialists, the sprint speed and good ammo economy as long as you have access to a survivalist's aura.

Melee weapon perks should be first + Elite or Carapace Damage (Maulers & Crushers are the only two elites that won't die from a revved heavy crit to the dome without it), then, probably Unyelding damage, for extra boss deletion or + Maniacs to 1 tap a mutie with a revved L1 crit... It's not as important as long as the Mauler - Crusher thresholds are met.
 

Horde strat :
Your revved L1 can cleave through lesser ennemies without effort, it's quite therapeutic... Vrrrrrr - Chop - Vrrrrrr - Chop - Dodge - Vrrrrrr...
If the horde is more mixed, you'll find that the revved L1 spam lacks a bit of oomph, untill you get enough martyrdom stacks. At 4-5 stacks, anything short of a Mauler will be pulped by a revved L1 crit to the dome. The attack will stick to specialists and elites, so be attentive to what you swing into... It's quite easy to get defaced by a pack of ragers if you clip into one of them without having the others controlled.
 

Single target strat :

Revved Heavy Crit to the dome, doesen't matter which one, heavy or dome... 
With or without martyrdom stacks, a crit to the dome equals a very dead elite.
A non crit to the dome will still mess up anything smaller than a rager. Critting only shortens up your "sawing time", making it faster, thus safer to use.
Bosses aren't faring much better... charging into one with a revved heavy and connecting with the weakspot would yeld substantial results, as Hadron would say.

Melee Elite Packs strat :
TLDR : Use stun grenades against big packs of elites, then use the single target strat.

Ragers are probably your main threat with this build. 
One is a joke, two are a challenge, three are a threat and four are a karking trap.
Even if you can now dodge out of a revving attack, it costs 4 stamina, and a dodge. Stamina and Dodges are your only defensive tools against a Rager in melee... 

So you don't want to charge into those fast attacking clowns without a plan to control them, because you may kill one each time you swing, but they can swing many times more than you do...

It's less of an issue with Bulwarks, Crushers & Maulers, although the time to kill of the revved attack is longer, they tend to over-commit massively on their main attack animations and you can deal with those using dodges only (I strongly advise against trying to block a Crusher / Mauler's overhead).
"Simply" create an opportunity with your dodges, dip in for a swing, wait for the kill, dodge back while revving, repeat. It's possible to handle 3-4 of them by dancing carefully. Remember that with this build, dodging greatly buffs the efficacy of our weakspot crits (Duellist).

Obviously, the stun grenades are your trump card against Elite swarms. they usually last long enough for you to 'thin out the forrest' to a point where the classic dodge dancing becomes a viable option. Don't waste them.


Closing notes : The new Mk XV eviscerator is probably the best recipient for a bloodthirsty blessing. Sure, the buff doesn't last long and you can't miss a swing without loosing it, but if you're ready to commit to the jank, the results are certainly there. I've averaged around 50% melee crit rate with this build... and some variations trying to fit in Enduring Faith (T1 right) 

(not worth the tradeoff unless you're really fond of knives)

(stunn grenade are a safer choice)

(taunt Ogryn synergy ?!)