So, the way Psychic Powers work is pretty different between Only War and Dark Heresy v2.0 ... since DH2.0 is newer, do you think that the Only War version should be replaced by DH2.0 if you have access to it? The powers are virtually identical, just how you use them has changed.

In short, if you are not aware, in DH2.0, the less power you exert the easier it is to get a successful cast of the power, just with diminished strength. The more Psy Rating you use, the harder it is to cast but the more powerful it will be (and the more likley to generate Psychic Phenomenon/Perils of the Warpity Warp)

If you can, I would say go with the DH2 rules. While you are at it, I also suggest adopting the rules for blood loss (and the Die Hard talent), fatigue, shocking, toxic, the damage profile for the omnissian axe, medkit updates, mechadendrites capped by toughness bonus, and repair/weapon mod rules. I would not port the requisition/quality rules, as the rules in DH2 for requisition are partially meant to capture the notable access of the Inquisition.