It'll be a bit thinner generally but I can't see that being a problem with a track car tbh. Not like its going to need a lot of cold weather protection.
The number is the distance the oil runs on a set incline at a set temp afaik? So the higher the number the further it runs so the thinner it is?Wrong way round is it not? Lower the number thinner the weight
15W 50 will be far thicker stuff compared to 5W 40 ?