A bigger cooler is the solution. The oil temp sensor is in the pan - the hottest point. Oil temps going back into the block need to be around 220-230F for best oil life and power. Hot oil, cool water. A lower temp thermostat is only going to lower oil temps until the cooler is saturated and can't shed any more heat - which is pretty much after a couple of hard laps on a road course. For the street or drag strip, you do not need any oil cooing upgrades.
E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
Vishnu PWM methanol custom trunk mount, Diffsonline 3-clutch Salisbury custom diff, Ohlins Road and Track coilovers, Vorshlag camber plates, much more...
E28 M5 w/ buncha stuff, R171 SLK350