I just purchased enough 10W30 Castrol GTX in 5-qt containers to get my up to 15,000 miles at 3750 mile intervals on the S2000, then I switch to synthetic and run 5000 miles, feeling confident of a full break-in on dino oil. I noticed HERE that 10W30 is especially touted as superior. In an overview they say "CASTROL GTX 10W-30 is formulated with superior base oils and patented additive technology to provide better protection against volatility burn off than other leading oils. GTX is the only leading conventional 10W-30 that provides this superior protection." Then they go on to list all the grades.