I would be concerned about 0w-20 or 5w-20 film strength breaking down at 300 degrees. Wouldn't want 0/5w-30 either. Sustained high rpms makes oil get really hot in apps such as towing up a hill or driving on the Autobahn. I learned this when my jet boat oil ran at 300deg F at a steady 6000rpm no matter what the water temp was. Turning up the cooling water to get the block stone cold made no difference. People without oil coolers were spinning rod bearings. I had to add a raw water to oil cooler to get the oil temps down. I guess what I'm trying to say is that a thicker oil is a crutch to get you through extreme situations when you have no oil cooler. I think that's why you see the European sports cars recommending much heavier oils. They know people are going to drive them fast for long periods, which we can't do here save for road racing. And those sessions usually last only 20 minutes.