@Turbo, I have both of those 1600 NBs shared in my profile. I did a little testing last night and they seem to be pretty similar in all aspects. I didn't notice a difference in handling characteristics, power delivery, gearing, exhaust note, lap times, tire wear, anything.
The only way we are really going to know if the 1600 NBs work with the NA is to get both on the track together and have a go. Maybe we can do a few practice races, one at a technical circuit and another at a power track (Autumn Ring Mini and Clubman), with all three models to really test the issue.
I would like to see the 1600 NBs be allowed to race in the series. It would allow for a bit of diversity and since the NBs are a tenth or two faster it would offer a challenge for the faster guys if they decided to stick with the NA. Don't get me wrong, the slight speed advantage the NBs have over the NA would be negated by the draft in a race setting, but in qualifying the NBs' speed would mix up the grid. I, personally, would stick with the NA in a three model field mainly for that challenge but also because I like being able to change my wheels and their color, drive from the cockpit view, and flash my brights at people.
What are the thoughts of everyone participating in this series regarding this topic? Everyone is welcome to test the NBs that are shared in my profile. Take them for a spin. Do some back-to-back test sessions versus your NA and see if you feel the NBs are a good fit for the series. Let's get multiple viewpoints and input from the drivers association.