[Hobbe]

What is the critical temp?

According to Castrol (we had a meeting with Castrol a while back) their engine oil products for BMW work well up to 140 degree C.
My car reaches max 125-130 degrees after being pushed hard for 30 minutes on the track (OEM intercooler replaced).
More or less the same temp as other BMW cars I race together with.
Hot? Yes, but not critical IMHO.

My old highly tuned MINI JCW GP reached 140 degrees rather quickly (small 1.6 L supercharged engine).
Adding an Mocal oil cooler (no OEM oil cooler on MINI) lowered the temp to 135 degrees.
Never had any problems with the engine even if the oil temp reached 135-140 degrees.
After five years and approx. 40000 km on local tracks the engine was still running great.
The best result was really to change engine oil every season, and to use the recommended SLX oil, which is what's recommended for 1M too.