When it comes to the mod loadout it is important to remember that a weapon should suit your playstyle.

Before we get started, I ask you to kindly review the build in full before jumping to conclusions. I have linked this build in Q&A chat and have been flamed for not having 200% strength, despite it working in Steel Path without issues. I find this build much for comfortable as it uses less energy than the average [Xaku]. If you don't like it then don't use this; there are many other builds out there.

This build has 150% strength and Breach Surge replaces [Xata]'s Whipster (Ability 1). Breach Surge blinds enemies providing a Stealth Bonus with a chance to release a surge spark. Blinded enemies are susceptible to stealth damage bonus, but are not vulnerable to melee finishers. Surge sparks have a critical multiplier of 1.5x, and can score critical headshots due to their homing properties. Stealth bonus below:

The Stealth Damage Bonus is affected by the rank of the weapon. Rank 30 weapons deal 700% bonus damage, while unranked ones only gain 100%. In between that the bonus scales linearly as per the formula:
Stealth Damage Bonus = 1 + (6 ÷ 30) × Weapon Rank
Bonus does not scale beyond rank 30.
More info on Breach Surge and Stealth Damage from the wiki.

I'm going to use an enemy with 100,000 health as an example.
The faceoff between 0% armour vs 700% bonus damage. Math gets janky here as 0% is better on single targets, but Breach Surge has map wipe potential.
If you do 100,000 damage with 0% armour you well.. do 100,000 damage, or you can can hit an enemy for 100,000 damage with 87.5% damage reduction for 12,500. 12,500 at 800% damage, (100% base and 700% damage boost), for 100k damage.

Enemies that have 87.5% armour reduction is the break point. If they have more than 87.5%, The Lost:[Gaze] (ability 3) is better, if it's less, Breach Surge does more. Keep in mind that run [Corrosive Projection] aura, corrosive and heat weapons. Bonus points for Breach Surge's chance to jump onto other enemies. This build uses The Lost: [Gaze] on def map and Breach Surge everywhere else.

Here's your typical [Xaku] [Gaze] armour strip use for Steel Path here.

Happy Hunting.