This is my personal version, hope it helps
there are basically 2 main kind of bosses, 6200 and 7700 armored. I'll consider armor penetration effect on the 2 types.
Bosses with 6200 armor
base reduction: 37% (6200 armor)
sundered 5x: 25,43% (3600 armor) - dmg increase for sunder: 18,36%
faerie fire: 22,07% (2990 armor) - additional dmg increase for fire: 4,5%
CoR: 17,11% (2180 armor) - additional dmg increase for CoR: 6,36%
Given the 3 debuffs listed,
Improved Expose in place of sunder: 13,9% (1705 armor) - additional dmg increase for Improved Expose: 3,87%
Armor penetration (175): 15,96% - additional dmg increase for it: 1,39%
Armor penetration (350): 14,77% - additional dmg increase for it: 2,83%
Armor penetration (800): 11,56% - additional dmg increase for it: 6,7%
Serrated Blades talent (560): 13,3 - additional dmg increase for it: 4,6%
Bosses with 7700 armor
base reduction: 42,17% (7700 armor)
sundered 5x: 32,57% (5100 armor) - dmg increase for sunder: 16,61%
faerie fire: 29,84% (4490 armor) - additional dmg increase for fire: 4,05%
CoR: 25,85% (3680 armor) - additional dmg increase for CoR: 5,69%
Given the 3 debuffs listed,
Improved Expose in place of sunder: 23,29% (3205 armor) - additional dmg increase for Improved Expose: 3,45%
Armor penetration (175): 24,92% - additional dmg increase for it: 1,24%
Armor penetration (350): 23,98% - additional dmg increase for it: 2,52%
Armor penetration (800): 21,43% - additional dmg increase for it: 5,95%
Serrated Blades talent (560): 22,81 - additional dmg increase for it: 4,09%
this is from rogue point of view, but looks like we are the majority among theorycrafters
If you wander what you can get to improve armor penetration,
All the ingame stuff available
as fixed stat
[Boundless Agony] (Dagger) - 210
[Choker of Serrated Blades] (Amulet) - 175
[Shady Dealer's Pantaloons] (legs) - 175
[Slayer's Handguards] (hands) - 175
[Slayer's Shoulderpads] (shoulders) - 175
[Stormrage Signet Ring] (ring) - 126
as proc on hit or use ability
[Madness of the Betrayer] (trinket) - chance to proc 300 for 10 scs
[The Night Blade] (dagger) - chance to proc 435 for 10 scs (up to 3x)
[Icon of Unyielding Courage] (trinket) - use: 600 for 20 scs (2 min cd, like 100+ flat)
[Warp-Spring Coil] (trinket) - chance to proc 1000 for 15 scs
[Badge of the Swarmguard] (trinket) - use: chance to proc 200 for 30 scs (up to 6x, 3 min cd)
as rogue talent
Serrated Blades - 560
Summing it up
you can basically achieve
826 (swords, maces, fists) from armor
1036 if you use daggers
1386/1596 if you have Serrated Blades talent