"If Jaguar have made refinements, I'd expect them to be in the low speed behaviour and alterations for presumably different rear drivetrain hardware"
S-Type is horrid at low-speed - the ride quality is /nearly/ as bad as a BMW and wet manholes are enough to get the ETC shouting at you.
The whirrs, clicks, pshhhes and whines/glurgs from the aircon/PAS/belts ruin the sound of the engine at low speed too. :-(
Absolutely stonking once out of town/on open roads though, to the point we had to remind my *mother* that (even if it was quieter and rolled less than her Rover 800 at 70leptons/hr...) 120 probably wasn't the most sensible of cruising speeds. Certainly no 'jitters' and not at all 'uninspiring' on the open road. The silly aircon/PAS/drivebelt noises get drowned out too, especially when it shifts (cam/intake?) at 5500 or so - luuurvely snarl. :-D
If you're looking at s/h ones the manual 3.0 V6 is the one to go for. At public road speeds its just as quick as the 4.0 auto V8, and hasn't got the horrible delayed/sluggish response the autos suffer from. Also won't have sat around at the factory before being sold - all 3.0 manuals (for the first 18 months anyway) were special-order only, and you had to wait an extra 6 months for 'em. Dealer gave up trying to flog us an auto V6 - even at the same price as the manual and with =A33k worth of options he wasn't getting anywhere. :-)
Old man and I met* one of the suspension designers who said although its the same platform there was masses of work involved to make/differentiate it as a Jaguar and not a Ford. Can't see a Lincoln or Scorpio comparing TBH, same way driving an R45 diesel you'd never think it a good enough chassis for a ZS180 V6...
Good cars though, if they hadn't made them ugly as sin (even the later ones...) or sold as many of them as minicabs the Omega would have had a much harder time.
*made a trip to some uni 3hrs away (all B-roads and twisty As...) to see a presentation by Jaguar, so that he could thank the man who chose the engine, 'box, brakes and suspension and throttle the snotty little kid who designed the body electrics and interior LOL!