What about your own X5's though?

Half the time I put in the UK's regular cheap stuff (95 RON) and the other half I try to find somewhere that sells Shell V-Power (previously aka Optimax) which is rated 99 RON.

Tending to go more for the V-Power at the moment since I doubt the previous owner bothered and it's meant to help clean the engine (2002 X5 4.4).

How many people can say they notice the difference in which fuel they have in their tank on these cars?

93 octane Ex on, Mobil, Gulf, Hess what ever cheapest

in my own car, i put 91(highest we have here aside from racing fuel) and i stick to the top tier gas stations.

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I put min 91 octane from Top Tier approved retailers.

I wish I got a BMW loaner (this is the 200th time Ive said that)

As for the Enterprise ones, since most domestics need regular, I give them regular. But if there was 10 feet of snow next week and I got a BMW loaner, than I would put premium.

Who is your service rep? I dealt with this old German guy in 04 and I never went back because of him. He doesn't work there anymore. I guess he retired. You would think a guy at his age would be nice. One of the worst experiences I have ever had in my 6 years of experience with service reps. He was rude and didn't take me seriously although I was a young 20 at the time; I was respectful the whole time because of the way I was brought up.

mmmm... I can, as with anything less than 98RON the detonation goes from any time under load below 60km/h to ALL THE TIME....

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I can on both my '96 Lexus and the X3. The ignition slowdown is especially apparent in the Lexus, but the X3 also runs a bit rough on highway/heavy loads and fuel economy suffers.

I was wondering something along these lines the other day. Does it actually cost me that much extra to fill up with the 'good stuff' since my fuel economy should also rise as a result of this.