Oils arent as major a factor now as they were "Back in the day". Used to be that certain oils had different proceses that made them better. Came from different locations, used different detergents ect. Now it seems that almost ANY oil will do the job. Personally, ive had good luck with mobil and a bottle of slick 50. Never had any complaints, and they seem to keep good lubrication. But as for crossing oils, how much does 1 quart out of 5 really make? the "advantages" are already dilluted in the quart, and then you dillute them with the other 5 quarts? Sounds like better chance for issues than advantages.