Not quite the same as standard house rules, so I felt this deserved a thread of its own.

In previous campaigns, I used bits from DH and pre-release DW in RT. And bits from DH, RT and BC in DW. Mostly gear, but some opponents especially in DW.

For a new Rogue Trader game, I'd consider Only War for plundering. The las strength rules and the weapons stats are obvious choices. Aptitudes could be great if I were willing to rework the system.

What do you all make of importing rules from the other 40k games?

Personally i'd be wary - While the different game lines may appear at first glance to be compatible they are so poorly balanced on their own that mix-and-matching the rules from different lines will throw any semblance of balance out of the window.

FFG are notorious for the stats for items changing from one book to another, even within the same game line. That's why we have such vast discrepancies as the las-weapon rules : they went from being sub-optimal in DH and RT, laughable in the power scale of DW and BC and then suped up to make guardsmen worth playing in OW.

Similarly things like the change to attack mechanics (Semi and full giving penalties not bonuses to hit) and Swift and Lightning attack function on Degrees of Success, can drastically change the balance in your games.

For a new Rogue Trader game, I'd consider Only War for plundering. The las strength rules and the weapons stats are obvious choices. Aptitudes could be great if I were willing to rework the system.

What do you all make of importing rules from the other 40k games?

I expect my next RT campaign to use OW rules for .. most things really.

Ship combat probably just RT/Mathhammer though.

I too have migrated to OW rules for all my 40krpg needs. They often disappoint, but not nearly as often as the earlier systems.

I swear, I'm like an abused housewife who keeps coming back for more.

But without telling us what "bits" you're gonna take from the systems, there's not much we can say. I say steal what you can from OW, except character advancement. The "buy everything you want" attitude from later systems really plays havoc with RT, usually leading to a situation where it's not so much that people *want* to buy Two-Weapon Fighting, Lightning Attack and Step Aside, but that there's a ~3000xp tax on being relevant in combat.

I'm mainly fishing for ideas on what imported rules other players and GMs have found useful in their own campaigns.

For Rogue Trader, I found the Inquisition-only equipment useful when bringing in certain NPCs. And a squad of relatively untainted traitor astartes made for a challenging final battle.

I use the Social Encounters in Tome of Excess using Profict Factor in place of Infamy

I use the Inquisitor's Handbook and Deathwatch rules for Unnaturals in place of those in Rogue Trader (which appear to have been copy/pasted from Base Dark Heresy before the IH Update which DW also uses).

As GM, I'll use rules specific to things which do not exist in the game setting I'm using (like Ogryn rules from Only War to represent Ogryn NPCs), but typically default to whatever is in the specific setting I'm playing in when two versions of the same thing exist.

It is always best to use the rules of your game setting as much as possible without mixing them up too much, or else bad things happen. If you want to use Only War rules in Rogue Trader, use Only War rules for everything they can apply to, keeping in mind they can't apply to everything. The more homogynous the rules are, the less confusing things get, the more balanced things will be, and the less books you will need to lawyer over.

As far as NPCs, monsters, xenos, weapons and armour, provided they are compatible with the rules you are using (and generally almost all of them are), you shouldn't run into too many issues, unless you try to throw a Chaos Space Marine Sorceror into Dark Heresy or a Purestrain Genestealer into Rogue Trader. As far as Only War weapons having more power, if the weapons are awesome in one setting, but the same weapons suck in another, pick the one that works best with your game setting, or the one that comes with it. If Only War las weapons are more powerful, and you want to use them, cool, but the mooks get them too to shoot at you with.