Zero. Because Well-Fitter or Sturdy makes you much much more resilient. Especially Sturdy.
Now if you don't plan to roll or block (low stamrecovery char in Gaze of Sithis for example), and you roll heavy, you can go for nirn/reinforced (whichever is more in full gold), to push for extra ~3k of armor, which is at least 5% - but since it's 5% mitigation that is close to finishing armor cap, it's even more.
Impen only matters in small amount of matchups and I don't really care about outlier cases.
@Larcomar Star gives -10% crit damage in mitigations. But that's like difference between, say, 140% and 150%, which would be 6.5% mitigation, and add crit chance on top, which would be ~40% for builds that don't invest in crit gear but invest in crit sources - you'll get 2-3% mitigation.
Now, when we say about playing vs NBs and their guaranteed crit on incap, in might be worth it, but on the other side, why would you just incap and not HA+incap? HA would eat damage boost then, if HA is made with DW only first hit will guaranteed-crit.
What else crits in the meta? Acuity isn't in the meta really, you can put it on plars but even there it is questionable, increased cooldown hits hard.
Crit build like what I'm assembling? Eh I never seen anyone doing anything like that.
Just natural crit chance? Well some people say that crit heavy-hitters like ults -> whip are what really kills in duels. Maybe true, maybe not. Idk, but I'd still boost active defences any day so I can block heavy hits.
And speaking about stars, those ones that give 10% mitigation from direct/AoE/single target are much better and much more reliable, as well as healing stars if they fit you.