Hi Jonathan, quite a bit of difference between the XK and XKR, so better if you can try them out and see if you have a preference. Other major decision has to be Coupe or Convertible, as that too will impact on your selection process. Engine size needs to be considered - the earlier cars were 4.2 litre V8, whilst from late 2009 the engine size was 5.0 litre V8.
Many aspects of the ride in the X-150 are down to personal preference. The cars look great on 20-inch wheels, but lots of folk complain about the ride being too harsh and seek out lesser diameter wheels. Note changing backwards from 20 to 18 is NOT possible on the XKR due to the size of the brakes / callipers.
The JEC has a Classifieds Section, therefore mainly Enthusiasts' Cars on sale, and in the December issue, there are currently 10 off X-150 cars for sale with an almost equal split between Coupe and Convertible, but in my opinion the Convertible is the better looking model. Nowadays the price range is quite dramatic, with some being advertised at under £10k and I have seen some on AutoTrader at over £40k.
Being based in Scotland, my own XKR Convertible is taken off the road (SORN) between October and March each winter so as to avoid the salted roads. Whilst the body architecture is all aluminium, there are steel subframes underneath and these can suffer very badly from corrosion, so be sure to look underneath any car you view - take a good strong flashlight - although most of the front subframe will be hidden under a plastic tray, but the rear subframe will be readily accessible to see. Corrosion of the aluminium body is always possible too, especially where stone chips have been present, or loose trim traps water and can vibrate through the coating.
If you want any additional insight / help, come back trough the Forum or drop me a PM.
N6 JMX