I agree with the post about using a Mondeo platform for the X type. The Mondeo lacks "badge" appeal, but it is a very good motor car.
I had a V6 3.0l Auto S type jag, and if I could afford another , newer one, I wouldn't hesitate.
Acceleration and handling, with traction control was superb. Without traction control engaged, it was huge fun.
Comfort and equipment as good as most, if not better.
Running costs astronomically high, as you would expect from the big cat.
People (Clarkson?) said the S type had strange looks, but like the 75, it's an aquired taste, and if you have a look at Clarkson , taste is obviously not his forte.
When pushed, on kick down, I was getting as little as 7-12 MPG, but with sensible driving, I could get around 20 MPG in town, and 27 or so at a steady 70.
The S type is a very different beast to the X type, and still has a more (gentlemans car) image when compared to the more sporty X type, but make no mistake, the "gentlemans car" can shift when asked, and the first of the 3 litre models can be picked up for a couple of grand.
My next motor will probably be an X type, but thats for financial reasons.
I should add (edit) that it could well be possible to get better MPG with a lighter right foot. Also, I sold the S type on, with 73,000 miles on the clock and NO mechanical problems. During my ownership, I had the AC pipes and a hose replaced under warranty, but I dread to think what it would have cost if I had been paying. One bad point, the earlier models had a tendency to rust on the door finishers. (usually matt black ,removeable plates between front and rear doors.
Good points? everything else, especially the electric memory steering reach/rake column which moved inwards and upwards to allow ease of getting out of the car when you switched the ignition off, and reverted to memory position when you got back in again. Class or what.
