Audi R8, Ferrari 458 and McLaren 12C i all faster body's than Ferrari 599.
Audi R8 and Ferrari 458 was equal in some testing
McLaren 12C could be even faster than those two.
But all these tests are for 2wd Unlimited and on 100cm and wider tracks. So might not be all correct towards Mini-96.

But the Mini-96 is between 17 and 17,5 m track length.
With other than box-stock or stock, how would your driving really improve?
Yes you get laps and therefor it will benfit you, but other than that, your tuning will not be very good for a larger / faster track.
The other way round seems too me to be better. Tune your car on a large / faster track and then run it on a small track.

But I am no expert and the good consistent drivers don't seem to mind so.