Just to let you know, there are different Zonda's in used car dealership.
There's two used C12's, one is nearly 1,000,000 and the other is around 350,000-400,000. Both can be tuned I believe.
The difference between them, other than the price, is that one of them is slightly older than the other, by about 2-3 years.
There is also the original Zonda, but this has less than 400bhp in standard tune, plus it makes the most horrific noise when you get near the redline.
I sold this, and bought a C12s.
I think the newer one will probably be slightly better on performance (NOTE: this is a presumption, not a fact), but I opted for the slightly older C12s and saved 600,000..
I haven't been able to add aero parts to either Zonda I've owned.