Mike, how would you compare the ST220 to your E39?
In short - far superior.
I have a 530SE auto which I px'd my ST220 against to get into and I've had no reason to regret doing so. The difference in ride quality is what initially stood out. My E39 offers a much softer ride, is far less crashy on poor surfaces yet also feels fully planted in the twisties.
On both cars the steering is sharp, responsive and reassuringly 'heavy' giving just the perfect amount of feel through the front wheels but the e39 is just, well, better.
Weight distribution feels more equally balanced in the E39. As good as the ST was through fast bends, the heavy V6 lump up front was noticeable, especially so under heavy braking.
Braking from high speed in the ST was scary. The BMW brakes inspire waaay more confidence.
My e39 is fairly base spec so doesnt have all the toys of the ST. I do miss heated & electric front seats but the BMW warms up astonishingly quickly from cold so I don't miss it massively.
The e39 cabin, interior plastics and leather are superior. Rattles and squeaks were ever-present in my ST220. The e39 offers silent bliss. Its an astonishingly well put together car. Even opening and shutting the doors on my car puts a smile on my face. They're heavy and they make a satisfying clunk when closing. The ST does offer more comfortable sport seats than e39 Comfort seats. However the leather quality is better in the e39. As I've never sat in an e39 Sport I can't say whether its Sport seats are on a par with those in the ST220.
The engines of both are brilliant but the straight 6 power delivery in the BMW feels more linear. You'll already know that you that the ST does its best work at the upper end of the rev range and needs to be gunned to get the best out of it.
The auto box is superb in the e39 and its a breeze drinving around town and in heavy traffic. I found the ST to be quite tiring to drive in heavy traffic due to the weight of the vehicle, its less responsive brakes and its manual box.
In terms of fuel economy, inevitably you're gonna get bent over in both. In heavy traffic the ST220 returned ~21mpg; my e39 is slighly less - maybe 18-20mpg.
The 'problem' with the ST220 was that the V6 was thirsty no matter
how I drove it. At least on the motorway the e39 repays me if I drive like a granny - which I often do. Stick the e39 on cruise at 70mph, lean back and reap some relative rewards.
The E39 Sport is obviously more popular than the SE but its harder to find outstanding Sport examples which are well priced. I actually paid a fair bit over the odds to get my 1 owner SE but its repaid me in terms of reliability.
An unexpected bonus is the copious number of wheel options available in a BMW. My Style 71's are going on this week and will give the car a very different 'look' I hope. Wheel options are limited in the ST although the standard alloys are great if looked after...too easy to kerb them though.
Moving from an ST220 to the E39 felt like a natural and logical progression, but if memory serves me well, you paid top dollar for your ST220 a few years ago. This makes the decision as to whether to take the depreciation hit a much harder one.
As good as the ST is, it's still a Mondeo. The snob in me likes being in an over engineered E39.