So long long ago I made another thread where I estimated that Justice improves your dps by about 10%. So today I decided to actually do parses while wearing various gear to find the actual improvements.
For this test I used Enraged, Cleave, and Unstoppable with a Strength Primary Brawler/Vindicator setup. I used a macro to just have my character spam Cleave for about five minutes so it would be nice and consistent ( and so I didn't have to sit there clicking for that whole time ). Here are the results:
So we can see that my earlier estimation of about 10% was pretty damn close. We also see that slicers gloves on their own are as big of an upgrade as upgrading all your mercs to GCR pieces, so that should make it clear why they're locked behind the OV grind - if they were on the GCR vendor they would need to cost as much as 3 GCR pieces. Also we see that the biggest increase comes from piling DUC and Slicers on top of GCR gear, where the multiplicative nature of these upgrades really starts to rocket things skyward.
Rando auction house gear -> Heroic & Determined 2ndaries
Switched to Annihilate for this
Comparisons of dps for various tank setups ( stacking Con, in tank role ):
Title says DPS but whatever, I'm throwing this comparison of mitigation in as well: