John, I had a BMW 530d before, and it did about 36mpg cruising at 85-90mph and it was the only car I ever regretted selling
I sold it to a friend and bought a XC90 thinking I would be all sensible
Anyway, back on topic, if your willing to downgrade(Prius or 120d) then I would wholeheartedly recommend Prius, it will cruise all day long at 80mph(but anymore than 90, it would sound strain), fuel consumption would probably be in the low 40's, I currently getting 50.3mpg round town(but I'm a gentle driver), cheap group8 ins, £15 road tax, and £90 service, I couldn't praise it enough
glad I didn't upgrade to an new X5 (although I'm still tempted)
Re 120d, only if your rear seat passengers has no legs....
As for CLS or Lexus...I can't see them being any better or cheaper to run than your current 530d. Unless of course you fancy a change...
All IMO of course
