Having been a 'petrolhead' for many years, owning a string of high performance saloons, I am afraid the time has come to change habits. With ever increasing fuel costs, car tax, insurance, poor road repairs and speed cameras everywhere, comfort and economy are now fast becoming my priorities. I intend to trade in my current M3 for a diesel and would appreciate your advice as to which car would suit me best? I cover about 18,000/20,000 miles per year, mostly on motorways and would prefer a 6-cylinder as I believe they are smoother and quieter than the 4-cylinder variants. I have around £25,000 to spend. Size is not the issue but comfort and economy and, to a degree, a bit of performance are, can you help?