As we all know,I`m a member of the thick oil group here. I drive my car fast and hard,the way it was designed to be driven,but I`m still very meticulous and careful with it. It`s never raced or abused,I just don`t granny drive it. Fellow Texans know if you regularly drive on I-35,80mph is the nominal average cruising speed if you don`t want to get run over. As per Z32 fsm,10W40-20W50 is recommended if the car is driven fast,raced,or in driven in hot climates,and 10W30 is recommended for fuel economy only. How well will 10W40 protect the engine vs 20W50 under said conditions?