Rotella 15w40

I read that the Rotella didn't past the last flat tappet or shear? test and the ford oil did. I think this was about 2 years ago so I've been using the ford stuff in the lawnmower and old cars. 15w40. But back in the day I ran Sunoco 10w40 in my race cars, everyday cars and everything and never had any problems. I've also heard Mobil 1 15w50 is really slick and great for race engines. I buy it at Walmart for like $23.00 for the big jug.