In Missippi you could probably use just MT90 and not worry about mixing. If you lived in Michigan where we have cold winters a 50/50 mix of MTL or MT90 is ideal. In Canada if you live near the artic area's 100% MTL is the way to go. I think last time I went 25%MT90 and 75% MTL to get even better cold weather shifting as we have had some really cold winters the last two years!