Thought I'd try V power.

[Dead Eye]

I run V-Power in both my car and thou as they benefit slightly from it. The car gets up to +10% efficiency on motorway runs (but it drinks fuel like no tomorrow anyway) and the thou just feels a little better on it - no increased power that I can tell. I mostly run it in the thou because of the enhanced cleaning properties and it helps be to earn points with their loyalty scheme

The 600 however seemed to run a bit worse with the 99 RON stuff. I reckon nick might be on to something with suggesting that the cleaning properties had loosened some crap and blocked the jets as my 600 has never been in good condition - something I plan on rectifying... eventually...