Shell V-Power in Sydney was pretty crappy to say the least. Caltex was much better and BP ultimate holds together with better economy (atleast in a pinging CU2). I discussed this several times in the past....
The additives in BP Ultimate has a cumulative effect on the engine and is supposed to improve combustion thus improving fuel efficiency. That's what I remember about it. Can look it up again if you wish.

Shipped the CU2 because they cost a bloody fortune over here LOL....Maybe I will trade it in for a BMW 5 Series LOL or a three year old Merc S Class....