I have been using Optimax since I bought my LCR (July 03) and have now changed to using V Power and I don't notice any difference. I think what people are feeling is differences in power due to the weather/temperature - some days my car feels like it has lots more power than other days - it's down to the weather conditions. I guess it might make a difference to a re-mapped engine, but the standard map wants 98 RON anyway - given that VPower/Tescos 99 are going to be at best 1 RON more, I can't imagine the performance difference will be that noticable.
Bob