[Closed] Shell V Power or BP Ultimate diesel fuel, does it make any difference?

Well their marketing blurb will obviously say it does but in the real world is it worth the extra pennies per litre? My local BP is flogging it at 4p a litre more than normal diesel so now on my 2nd tankful in a 10 year old van. I'm sure it really does now run smoother, quieter, less smoke (haven't measured mpg economy yet) - Mrs says it's because I want to believe it and it's the placebo effect. Anyone else use it?