I've also read dozens of UOAs and a recurring trend seems to be that EJs are not very happy with thinner oils. So I made an appointment with Bren Tuning for the 30k maintenance for: Walnut Blasting/Tranny Svc/Rear Diff Svc/Spark. The past few months I was experiencing some unusual detonation issues that even resulted in my DAM dropping. Motul Oil for your Subaru 100 Synthetic lubricant (Mid-SAPS), specially designed for Diesel Particulate Filters (DPF) and Three Way Catalytic converters. Refer to BMW recommendations when in doubt. I have been running Motul 5W40 X-Cess 8100 for about 30k miles. I'm siding with Subaru engineers who put an oil cooler in there and just use the best SN-RC GF-5 oil I can find, not a high HTHS oil for no apparent reason. BMW LL-01 lubricant such as MOTUL 8100 X-cess gen2 5W-40 is required. I don't think using Motul or Rotella T6, as you're planning, will do anything to damage your engine.
Some say they don't care as long as the oil "looks OK on the dipstick", and some say they will demand the correct Owner's Manual spec be used exactly. Whether Subaru will enforce that is up in the air, since I've heard stories that go both ways. According to the Owner's Manual, which apparently nobody reads, you need a 5w-30 full-synthetic that is SN-RC and/or GF-5. Except all the oils you choose don't meet warranty requirements. I'm using a 5w30 in an attempt to keep Subaru happy under warranty.