Not sure I understand what you mean with the car part. Sprint races are run in GP2 with cars that have no DRS and durable tires, so even less overtaking. With FISI car, DRS + fragile tires, the sprint race rule actually makes much more sense than in GP2, as there will be both overtaking and the tire element even in a 30% race.
Also I'm not following why a 75% race would be that much more exciting than 60%, it's a difference of around 7 laps. We have tires that do not last for much longer than 10 laps on tracks like Sepang. There will be different pit stop strategies regardless of whether it's 60% or 75%.
If I'd want to sign up to a GP2 league I would do that. I am here to run a F1 car and a sprint race in a F1 car makes no sense. I am pretty sure you wouldn't sign up to a league which runs 30% races with F1 cars neither and many of other drivers too. Don't really want to sound harsh or anything here but doing it just for the sake of copying a GP2 class it still makes no sense with this car. I at least am not interested in running the 30% race.
I'll probably do the 60% but just leave for the 30% race.
Maybe with 60% you will see different strategies on few tracks but not as much as with 75% for sure. I guess that will get clear in Bahrain anyways.
With 75% it's pretty clear that we would have more options on strategies.