^I don't think I buy sleepwalker's argument,.. at least not 100%. I'm pretty sure you could put an ordinary text book in an oven at 250* and it would probably last a decade but it would burst into flames at 500*.
Testing an oil at a temperature 2 or 3 times higher than it will ever see may not yield any useful results. We need to know how an oil performs in a real world environment with dust, dirt, humidity, extreme pressure as well as high heat.
Just because an oil breaks down or burns at unrealistic temperatures doesn't mean it doesn't perform its duties well in a normal or even extreme environment.
There may even be some unwanted side effects of an oil that simply doesn't burn. (perhaps it's the additives like detergent or seal softeners in high mileage oil that burn more readily and would have to be eliminated to create a heatproof oil ???)
Engine oil is supposed to be replaced at least twice a year regardless of mileage so there is no need to extrapolate past six months service.