I do a regular run of 440mile round trip and average around 30k miles a year.
There are a lot of variables here and comparing "XC90 to XC90" just won't cut it, different tyres, different servicing, different oil, different tyre pressures, different weather conditions (Wind direction of drive etc etc) You will only be able to see the benefits of your own car on your own car on your own route, on a regular basis...
But what I can tell you is... If I run 2 x tanks back to back on V-Power I generally get an extra 58 miles in a tank, there also seems to be a long-term effect by doing 2 tanks back to back where if I change back to regular diesel after v-power I can keep getting slightly better mileage for around another 3-5 refuels...
If I just run 1 x tank of V-Power it has some benefit but nothing like running 2 x tanks back to back.
Anyway, that's my 2p worth based on my XC90 and BMW 116D
Without a doubt though the biggest user effect on fuel economy is tyre pressure!
I also did a challenge once of how far a couple of us could get on £15 petrol in a Mini 1.6 (BMW), I did 312 miles by sitting behind a lorry on the motorway and "drafting" it, the other guy did 228!
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