Speedbeties
 Arbites Build - Warhammer 40k: Darktide 

This build is for rollin' around at the speed of sound.
You've got places to go, gotta follow your rainbow.

General Strategy:

You are no longer an Arbitrator, you are a Zealot with a law degree (and a dog).

This build is made for one thing, and one thing only: hoovering up those delicious tech remnants in expeditions. Your main strategy should be running past every enemy and onto the next objective or the closest Salvage/Tech Remnant. Occasionally you should turn around and mark one of the elites or specialists following you so that your dog can have a snack (though he'll eat plenty on his own).

Let's cover the Talents that enable you to be Hadron's greatest asset:

Talents:

No Escape - 10% movement speed for 4s on elite/specialist kill. 

Rapid Movement  - 5% sprint speed for 5s after a slide. You should already be sprint sliding to conserve stamina and stay above 50% as often as possible to have Stripped Down active. Additionally, this talent also enables you to regain stamina by 5% on kill. 

The really cool thing about both of the talents above is that your dog will kill enemies on his own with no input required from you and these kills also proc these abilities. Extremely useful when carrying a data reliquary halfway across the map to the extraction door.

Not Far Behind - 10% movement speed for 5 seconds when your dog pounces on an enemy. Your dog will automatically pounce on the stormtroopers behind you, so no need to worry about marking enemies too often. Try not to mark enemies that can't be directly pounced (crushers, bulwarks, reapers, mutants, hounds, armoured pox hounds, bosses) if there are other targets available as your dog will take longer to wind up for another pounce.

March - 15% movement speed for 3 seconds when you shoot (not kill!) an enemy. Dump one or two rounds into the guys in front of you while you're sprint sliding.

If you can get all 4 of these up at the same time that's a bonus of 40% movement speed. You will be flying.

Your Problem Solvers:

The Vraks Mk V Infantry Autogun may look like a gun, but it's actually a speed machine. With 80% mobility you will have a 0.60 boost to your sprint speed. Allowing you to really make use of the talents listed above. You should not be using this gun to kill, only to shoot to occasionally proc March. With Stripped Down you are immune to ranged attacks while sprinting with more than 50% stamina, this is what allows you to essentially ignore ranged enemies because if you play this right, you should almost always be above 50% stamina and sprinting. What's going to stop you from doing that? Enemies getting in melee range. 

The Branx Mk III Arbites Shock Maul  has such high damage output that you don't really need to focus on trying to increase its effectiveness against anything besides ogryns and bosses. Any time you can't run/dodge out or you need to hold an objective, pull out your club and get to bonking.

The Arbites Grenade is just there for fun and so you can spend all your salvage quicker than mag dumping at the ammo crate, use it to get out of a pinch or create space to start your next half marathon.

Slow downs:

Unfortunately, you will be in situations where you will have to slow down, or God Emperor forbid, stop entirely. 

Reloading is barely a problem, but it is still a problem. That's why we have Speedload  and Judicious Efficiency to help you out. Just mag dump into the crowd following you and you'll be good to go for a reload.

Getting cornered is almost never an issue. You have your Branx Mk III Arbites Shock Maul  and Castigator's Stance combined to clear the obstacles in front of you.

Toughness being depleted should not be an issue as you should be able to regenerate toughness through running away with Walk It Off  or by letting your dog eat with Canine Morale, Up Close, and Part of the Squad. If those strategies fail and you need toughness right now the best way is to use Force of Will + Concussive to kill a horde or two so that you can continue on your way. Castigator's Stance if you feel you might be close to death. 

The only thing that can really kill you are Scab Trappers . So prioritize them as soon as you hear them and you should be fine. Your dog will rescue you from all the other disablers.

Alternative Ranged Weapons:

(Blessings only - Perks remain the same)

Weapon - Blessings - Dump Stat

Ius Mk IV Shredder Autopistol  -  Inspiring Barrage  + Speedload  - Collateral

Agripinaa Mk VII Combat Shotgun  - Hit & Run  + Terrifying Barrage  - Stability

Crucis Mk XI Double-Barrelled Shotgun  - Hit & Run  + Terrifying Barrage  - Reload Speed

Godwyn-Branx Mk IV Bolt Pistol  - Run 'n' Gun  + Lethal Proximity  / Puncture  - Stability

Agripinaa Mk XIV Quickdraw Stub Revolver  - Run 'n' Gun  + Gloryhunter  / Speedload  - Reload Speed

The marks linked/listed above don't necessarily need to be used. I generally prioritize damage > ammo capacity > reload speed, but these are my primary factors on choosing these marks in particular.

Alternative Curio Perks:

Instead of revive speed you can take either: 

Gunner Damage Resistance - To help keep your toughness up when you're sprinting with the Data Reliquary and don't get the benefits of Stripped Down. 

Corruption Resistance - To help you survive longer after the timer runs out, but 9/10 times you're good. Especially if playing on Heresy. 

Alternative Melee Weapons:

Anything you want. Just have some decent horde clear, be able to hit headshots consistently, and it needs to have a way to put out boss damage since your gun will be a peashooter.