I see what you are saying completely. Truth is when I returned to the hobby one of the concepts I kicked around was a "Re-Inventing Fear" style Iron Warriors project, and loved brainstorming Berserker concepts. To me the cold, calculating brain of the Iron Warriors would look at the bretheren falling into Khorne worship as "having episodes" so to speak. Throw them into a unit and have them be the "hammer" to another units "anvil" in the trenches you know?
I love the gore idea from Space Marine. Have you thought of doing it in degrees? Perhaps the newer members of the unit show disturbing habits that made putting them into the unit needed - like taking a gore covered hand and smearing the blood across their helmet, chest, a shoulderpad. Maybe also in terms of modelling converting some Black Templar arms? The ones with chainswords chained to them?
Love your project and you (along with good ol' Chrono) are synonomous with Iron Warriors in my head. Figured since I'm not doing anything with these ideas I had maybe someone would take em or leave em. ^_^