I know this has been covered a ton and 5-20 is safe but I would really like to use 5-30 synthetic instead of 5-20 that is called for in my 06 Hemi Dodge Ram 1/2 ton and a Mazda MX-5 convertible. No warranty left on either. I guess I just like using the 5-20. I would like to know if the 5-30 is safe. What do you think?