Having just finished a fairly high powered Dark Heresy campaign and planning to move on to an Ascended game at some point in the future I have discovered that I have problems with the way penetration and armour work. I find that if you have high end weapons (Plasma guns/power weapons/melta weapons) armour is largely irrelevant as the penetration rating of such weapons makes it pretty much useless.
I don't just want to start boosting armour ratings as a counter as that would make bolt guns/hellguns more useless that they already are so I am looking to see if anyone else has come up with any house rules for this (and hopefully playtested them!) before I have to try and write my own