I have a 30 row oil cooler with a 14 inch thermo that switches in automatically at 80c, I also run the stock water to oil cooler.
Most of the time my oil sits around 70 - 80c, even in winter, but I still got the oil up to 140 odd at Sandown on a 30 degree day, after only 3 laps. The water was at 145 though, I probably should have turned the boost down.