So I would like to set up a titanic set-piece battle where a kill squad take on one of the greater daemons from Mark of Xenos. Those are double-hard bastards though, and I'm not sure what Rank or XP level the marines should be at if I'm not looking for just an instant TPK. So! Who has gone up against one (or more!) of the Greater Daemons with a squad of marines? What was it like? What was the scenario, and what were the circumstances of the encounter? How did it play out, and what would you pass along as tips involving this sort of battle? Or maybe you ran an encounter like this?
When the stats get as high as they do here, it's hard to just eyeball it - and I'm a stickler for good encounter-design, too, so I'm looking for any insights that we can share.