Mike,
To answer your question earlier. Both cars are great in their own way and a slightly different drive to each other. The AC had a really good test when we joined the SMF Monte Carlo or Bust run, last year. This covered all road types and we were pushing quite hard. The AC was brilliant and kept up with everybody, no problem. Performance on twisty back roads flat out was outstanding, cornering was 1st class taking "S" bends easily at around 70mph. I said we were pushing..!! The car did not miss a beat and was comfortable the whole trip.
The 4200 so far has not done such a long trip, only a few hundred miles at a time. There is a difference, still a firm ride and well planted in sport, I do need to drop the suspension a few mm, as there is a fraction more roll compared to the AC, but not much. The 4200 feels heavier and more planted on motorways. Power wise the 4200 is fractionally faster, but the acceleration is different. The AC when the turbo's come in is manic, the 4200 is smooth power right through the curve. The 4200 is comfortable just like the AC. A few more little gismo's on the 4200, the satnav is a laugh a minute.
It is quite hard to say which is the better car, as they both have their attributes and are a slightly different drive to each other. I think I would say that the 4200 just has it's head in front, but not by far. I do like the CC box in the 4200, changes in sport are lightening fast and the power is smooth. 0-60 is a touch better in the 4200.
It's a very close call though.
Cheers
R