Thought I would offer a brief follow up some 10 months later, I do dip in and out here from time to time.
I wish I could report back that I made a terrible mistake and that I miss the BMWl Afraid not, and after driving an F10 (another 518d!) recently it really shows where the Superb is superior, though people here may not like to hear that!
Ride comfort: The BMW jiggles all over the place (SE) and always feels too firm, the Superb suspension and tyres are much more complaint and small imperfections are barely felt. In the BMW you feel every little bump at slower speeds. I have no idea how it rise so poorly for such a heavy car. At speed and on the motorway it finally settles down.
Refinement: Petrol V N47, no contest. haven't missed that rattly diesel engine for 1 minute! Things level off at speed, where the BMW and Skoda are very close.
Running costs: The Skoda has not required much other that routine servicing so far. The BMW needed all sorts of work under warranty done in the same period of ownership. I did replace the pads and disks, the Skoda discs are rubbish, prone to rusting, total cost €300. What would that that cost in the BMW, €900? The Superb is a bit more frugal, 6.1l/100 v 7l/100 in the BMW.
What I enjoy most though is peace of mind, I don't worry about parts failing on the Superb, and if they do they wont break the bank to fix, I don't think about rusting doors, EGR's, or fishing leaves out of the bulkhead. It is more spacious, the infotainment is better than iDrive, everything just work so well, VAG are very good at this.
I do still look at F10's, I love the look of them, with the right wheels and spec I think it is a great design, I still think the interior is beautiful and I miss that sense of luxury. But for me the truth of it is the F10 HAS to have straight 6 petrol with VDC to feel special in the engine and ride department. Otherwise it is just too average.