I have a 98 cobra with a S-trim. New motor has about 2500 miles on it. I have been putting 10W40 castrol edge in it. I want to change to Amsoil or RP. I want to go with a 10W30. Will there be a problem going to a 10W30? I looked on both web pages and it seems like they both have a few types off oil to pick from. Whats the best type for each? I drive the car most of the year. I also have a D&D viper spec T56. What is best to put in it?Thanks for any input.