how do you know which is more robust, as you put it?I like to use the best oil I can obtain. I like the peace of mind knowing I can go longer between changes if need be and maintain a very clean engine. There are times, especially during winter, when changing the oil is a hassle. I prefer to spend the extra money for a more robust product. It's as simple as that for me. Oil is not expensive. Never has been. Of all the things I purchase I'd put oil at the bottom of the list. So oil price is inelastic to me.