Generally NPCs are a little higher, I'd say (this is based off the last time I checked the differences) +5% maybe 10%.
More that the skills and talents are more different than 1st over characteristics.
Get 2nd ed or tweak 1st ed?
Hey guys!
Since you are wondering about all kinds of issues with the DH 1st ed. and DH 2nd ed, I do suggest that you take a look at this carefully replanned Advanced Dark Heresy 2.0 (2.0 referring to that this a second iteration of this ADH, not that it actually is totally about DH 2nd ed.)
The Advanced Dark Heresy features the Dark Hersy mechanics but redesigned in creative ways that also have seen many play test sessions and lots of thinking. There is better description to the features of this system in the discussion I linked below.
Link to the publication thread of the Advanced Dark Heresy 2.0