My buddy got Only War for Christmas, and we started mucking around with it last night. I'd had a chance to look through the Beta, so the whole thing wasn't very new to me, but it renewed some interest. I'm fully aware of some other conversion efforts, so bear with me.
After our breif intro game last night, I sat down and started comparing classes from DH to OW, and the results were a bit shocking. To sum it up, OW characters are about 1500 xp higher than DH characters, using soft conversion (hand waving some things like differences in Weapon Training). Aside from a few skills here and there, the most striking differences were the large number of freebies that come from OW regiments. There are a number of free talents and skills given out in excess of what we see from DH home worlds. While some of this can be offset by drawing a comparison to background packages, it fails to address one key difference: characteristic bonuses.
Every home world in OW gives a few characteristic bonuses, as do every specialization. Additionally, they seldom have a characteristic penalty. For example, DH hive worlders take a hit to Agility. in OW, hive worlders not only do not take a hit to Agility, but they may even get a bonus to it. Unfortunately, not a lot of home worlds exist between the two, and my copy of Inquisitor's Handbooks was elsewhere, so I couldn't get a good pool of data.
Anyways, I took some notes and went to bed. After reading through some of the conversion efforts here, one issue became apparent. Most people doing conversions seem to be content bringing DH characters into OW on the higher scale presented there (that approx. 1500 xp difference). I'm not sure how that sits with me. What people are presenting is the almost wreckless (compared to DH) offerings of characteristic bonuses here and there. I find myself on the other side of the fence, and more interested in stabilizing DH than buffing characters. Not that they don't need it, mind you, but it's always easier to add more xp than it is to take it away.
So for me, this is more of a directional concern. Should the lovable hobo-acolytes be buffed up to OW level, or should we be concerned with bringing the more stable OW rules to DH? In other words, are we bringing DH into OW, or OW into DH? Everyone seems to be taking the "DH into OW" approach, where DH material is improved and raised to the aforementioned scale. Nothing wrong with that, but I'm curious what it would look like to bring OW qualities like Aptitude advancement and usable combat into DH and "keeping the acolytes down," so to speak.