So I've owned both cars. I had a
2.5 X type and am on my 2nd S type. Both cars are fantastic but for me hands down the S type wins by miles. So you've test drove the S type i would now go and test drive the X type. Personally I think the no it's you sit in the X after driving the S you would feel the same. The S is way superior but it depends what you want/need from a car. My favourite thing about the X type was the permanent 4 wheel drive which in the winter is extremely useful. This I believe is only on the 2.5 or 3 litre engines. The X was built on a Mondeo chassis when ford over took jaguar. Which isn't a bad thing as such but I've owned Mondeos before and if you have yourself or atleast driven one your notice lots of little Mondeo bits and pieces inside the car. I.e light switches, clock, handles etc. Only minor things but you would definitely recognise them which for me sort of ruins the whole point of owning a Jaguar.
I just bought myself another S type just before Christmas. 3.0 V6 Sport and absaloutley love it. So glad with the purchase. It was between the S type and a BMW 5 series and would always go Jaguar from now on I think.
This is all only my personal opinion as I have owned both cars. I would definitely test drive a couple of different models of each car. And if you can afford a newer version of a certain car that's normal for a reason. A slightly older car didn't mean anything if your buying something like a Jaguar. If it was a Vauxhall Corsa I then it would bother me. That said alot of the X type is based on a Mondeo so I'm turn it's great for spare parts if ever you need them.
Be interesting to know What your final decision is and why so if you go through and make a purchase let me know what you went for I'm intrigued.