I've tested Shell Optimax, BP Ultimate and Mobil 8000 to as close as ideal conditions as practical (ie. Firstly, I put a full tank of one, reseted the meter, then when the tank was empty, I poured another tank of the same fuel. Then it was tested over two full tanks. I then did this with the next type. Secondly, I drove as consistently as I did, and much the same route for 6 weeks. This includes seeing my gf every second day and only driving at the same times).

From this, I found that BP Ultimate came on top in terms of performance and smoother. Ie. It feels quite quick the throttle response compared to the others, where I felt a bit laggy.

In terms of economy, Optimax came on top but no greater than 0.2L per 100km. However I found that the car tends to be less stable than Ultimate or Mobil 8000.

I'd personally rate BP Ultimate, and Optimax and Mobil 8000 as equal.

However, given the $$$ factor. I pour on normal unleaded most of the time..... with the good stuff once a month.