I was wondering if octane booster can be used safely in the RS6. I have a few bottles of NF Race formula from my old car, and I will be travelling in areas where I may not be able to find super unleaded.

Has anyone used it, and if so, how much?
Maximum strength will be +6 RON, which I'm sure is ok for 95 RON NUL... but what if I use it with Tesco's 99 RON?

Thanks.