Do you know that your flame trap (like a PCV valve) and its related hoses are clean, not gunked up? If that's clogged, you will burn more oil than normal and it's often neglected on 850s as apparently most people (including most techs) never check it on a regular basis as it's not as problematic as it use to be on the older RWD Volvos. On FWD Volvos, it's often totally neglected until there's a problem with oil consumption or leakage and seen at higher mileages. I've seen several in the last few years where it was clogged and causing problems. I'd check that long before assuming that you have serious engine problems which are unlikely unless abused, poorly maintained and/or overheated. I have seen major engine problems due to poor maintenance (like serious lack of oil changes).