I've had a bash at this one a few times before.
I run a 156 2.5 V6, which as i have found with all petrol cars, the V power IS better, full stop.
But in my 2.5cdti Remapped Movano / Master, the V power diesel makes not a jot of difference, and nor does it in my 156 2.4 Remapped JTD.
I do have the opportunity, in the van especially, to test over long range mileage and use, and i have found that normal, quality branded diesel, will do as good a job as it gets, particularly if i keep the injectors and system clean with the addition of a cleaner like redex if i know i'm going to do a few hundred or more in a day or so.
the extra price of the V power diesel is in no way shape or form compensated for by any extra mpg that i have found.
even in white van mode, i drive sensibly but properly, appreciating safety and speed alike, and always have an eye on the guages and figures because i'm tight! ha ha!
In My Opinion and Findings...
V Power petrol ROCKS!
V Power diesel SUCKS!
and is a way that Shell are trying to capititalise on the popularity of the petrol version, but actually extort us by selling us nothing diferent or better whatsoever.
I do also have a source of information within the petro-chemical industry, who will tell anyone that'll listen the few important and incredibly minor differences between these types of fuel, normally in the form of an extra and unnecessary additive to an already incredibly diluted cocktail of unburnable chemicals to form a sort of combustable fuel, that altogether make sod all difference, but keep the greenies happy.
My advice, a shot of redex every few thou, very regular oil, air, and fuel filter services, and don't forget to drive it like you stole it every now and then!!!
oh, and hang the hippies!
bloody greenies have cost us a fortune since their inception, and have and will do nothing to save the planet at all with their narrow minded short sighted fixes to problems that don't even exist!
PHEW, thanks for the chance of that RANT, i feel a whole lot better now!!!