Hey Tim, I went from a big 4x4 to the Clubman D so it felt like a supercar in comparison! I know that doesn't answer your question but I think you will get used to the difference quiet quickly.
Iam running 17inch rims on standard suspension which gives a nice balance of comfort and cornering ability, the sport button was the best £90 I've ever spent, well worth it, I have it on all the time unless Iam on a motorway.
Even if the cost of running a diesel ends up the same as running a petrol due to fuel prices I think the D is worth the extra money just in performance alone over a petrol, and that's without congestion charge and road tax savings.
John