You could make things interesting by having the last 6 rooms empty, or perhaps with an intriguing puzzle to solve instead. That way they'll walk into the room thinking there'll be a battle and find.... nothing. They'll get suspicious and check things out a bit more cautiously, always expecting something to jump out at them, and it'll be enough to keep them off guard, as well as giving them some much needed breathing space.

Puzzle sounds intriguing, what type of puzzle would you think could be interesting? I have this dark tech that resonates tearing anomalies that break down the surrounding warp and controls the power and life support systems but I have at least two or three encounters where the players have to fix things using tech use and logic skill tests. I guess things can go horribly wrong for the players such as lights turn out, doors stay shut and not only will the players have to battle aliens and daemons but the whole Fortress/Station is possessed by a daemonic machine. Part of the story line part puzzle.

Sorry for the slow reply.

Actually, I don't really know of a hard and fast rule or easy mechanic for determining this. I suppose you could always use the Threat Rating of each entry in Creatures Anathema, bearing in mind that the characters in each RPG begin progressively
stronger, so that a 1st level RT character is the equivalent of a 5th level DH character.

It practice I'm told that seldom works out but I haven't tested it out for myself.

Sure...and with having 4+ players possibly, the players having toughness and armor, effectively hitting them should be challenging or average. There is also the opportunity that some of the players have taken swift attack and will hit twice with ranged weapons and do more damage if they exceed on semi or full auto. This means to me that more monsters would be an effective encounter. Maybe raising that to 2:1 for every player double the monster. Not always but I guess looking at weapons of monster, soak of monster, weapon quality and talents with traits should help me determine the numbers.

Definitely. I just wish there were an easier way to gauge it quickly.

I know....Make an overall Bestiary and encounter formula would work. I think this is something that FFG would do justice to the players. I know 40k is gritty but I have in the past went with a 1:1 ratio of monster versus men and it just seemed that the player characters are always built tougher than the monster. I think applying traits, qualities and talents we as Game Masters can effectively make a challenge to the players involved. I mean in the Grey Knight game just their Nemisis Force Sword does 1d10+19 damage with a a pen of like 5 or something. Yeah Lord there has to be a way to make a challenge to the players.