An old FORZA from years ago covered the differences between these cars. They mentioned that a Series I car in european spec was the fastest and best handling, yet the most basic (sounds like the 365 BB vs. the later Boxers).
I think that along with the Dino badges make it the most desirable. I wouldn't want Ferrari badges on that car. Not that it's not worthy, but because it makes it more unique along with the Bertone logo
Anyone have experience with a Series I car?