Depends on how close to the limits the car is set up. I always encourage people to bring their car in for mapping on the worst fuel they are likely to run, so if they can't always get V-Power and sometimes use BP Ultimate, I get them to have it mapped for Ultimate.

Forgetting scientific tests and so on, we absolutely positively see higher knock readings from BP Ultimate than we do from V-Power. I wouldn't put it in mine now at all and I used to swear by it.