I drove the 2.7 TD Premium Luxury Auto XF, which isn't necessarily a fair comparison to the GS450h due to the engine. Although the first GS450h i've driven was the totally abused one I saw today.
• XF had more road noise, and a much firmer ride
• Engine very noisy in the XF, it felt slower than my IS even though its not supposed to be.
• The interior is very space age on the XF, to the point where its quite a wall of silver buttons, I think I would get used to this though.
• The GS has more room in the back, the XF was ok (it solves the problem the IS has of no rear legroom when i'm driving), but in the GS I can fit behind myself driving, and i'm 6ft 4.
• The XF had rust on the boot lid! I've not had a car with rust on since the 90's!
• B&W audio system was nice on the XF, a warmer sound than the Mark Levinson system in my IS which I think can sound a bit aggressive.
• The XF, at least to my eyes, is the better looking car.
Overall I learnt a couple of things today, the XF isn't for me, the GS is my next car.
As a said before even this abused one drove nice and smoothly, you could feel the power available. It seems though the cheaper cars are not going to be up to my cosmetic standards, so when i do a tour of cars next weekend i'm going to line up some lower mileage examples. My IS looks pretty much new inside and out, and thats how i like it.