Funny you should say about an XJL Supersport as I have had one for 4 years and just listed mine for sale as I bought an E43 Estate recently to replace it with. Absolutely love it. I've had a few E Classes but never an S Class. Always loved the X351 XJ and I couldn't resist the value that the XJL Supersport offered at the price compared to other options I was looking for at the time.
I aluminium bodied XJ with that 5.0 V8 Supercharged engine mated to the 6 speed ZF auto is a great combo IMHO. Good fun to drive, cheap to buy, run and service. Very quiet, comfortable, spacious, safe, well spec'd so I don't have many or any downsides. I'd love to keep it but I'm rolling two cars into one which is why I have just bought the E43 Estate so it has to go.
Feel free to ask any questions I have got to know the car quite well after owning it for the last 4 years.
Will be trying the XJ this week (if its available) - so will see how it goes