Exactly the same thing happened to me at the track: limp mode under hard braking and in turns, but only when oil temp exceeded 250F.
Sometimes got CEL, which persisted even after restarting the engine; went off after a couple of minutes of waiting with the engine off.
Gonna pull the error codes tomorrow and follow-up.
marty-k, did you get the chance to find out what it was?
E92 335i M-Sport | Bilstein B14 | H&R ARB | Quaife LSD | AR Design oil cooler | Tarox Sport rotors | Carbotech XP8 | Toyo R888 | OZ Ultraleggera