I posted about this in the PTS forum to show my annoyance with seemingly every other class getting buffed set bonus while Jugg tanks still had the exact same (PTS forums are now wiped, wishing I had archived my post). With Force Scream on a 12 second cooldown, a mostly 72 Jugg tank will absorb 1252 damage, or 104 HPS without the set bonus. With the 4 piece set bonus, you gain an extra 21 HPS for a total of 125 HPS from Force Scream.

I remember doing tests with all the free Arkanian on the PTS. The difference in threat was that with 4 willpower armorings you pulled 90-92% of the threat you would with strength armorings. I then worked out that you lost about 5 HPS from Force Scream (each bubble absorbing about 1190) when you had 4 willpower armorings compared to 4 non-set bonus strength armorings. That means as a whole, going from 4 Strength set bonus armorings to 4 Willpower armorings causes you to lose 25 HPS from Force Scream (note, this is independent of how hard the boss is hitting).

The question then becomes how hard must a boss hit for the 25 HPS to be outweighed by a 2% overall DR? Well, for pre-mitigation DPS above 2381 for 90% accuracy melee, and pre-mitigation DPS above 1429 for Force/Tech attacks (Kinetic/Energy damage), the Sin's set bonus mitigates more than the Jugg set bonus on a Jugg. To put that into perspective, that's 500 DTPS for the melee case and 497 DTPS for the Force case after mitigation. Now considering we're getting hit for 1200 DTPS or higher after mitigation, the Sin set bonus really starts to take off. At the 1200 DTPS level, you're taking 30 less damage per second with the Sin set bonus.

So at "normal" damage levels, you knock off 30 more DTPS with the Sin set bonus. You're threat is reduced to 90% of what you're doing with strength armorings though. You also lose 1 second of Blade Turning and Invincible is 10 seconds instead of 12. Worth it? I've already got 2 Underworld Sin tank armorings in my cargo bay while I wait for 2 more drops.

I personally would not go for the Sin tank set bonus as a PT. The threat loss will be much larger as PT's don't use Willpower as a secondary stat. And even though they'll mitigate more with the Sin tank set bonus, the PT set bonus at least scales with incoming damage levels.