I've tried super before and not really noticed any difference. My MGB was quite particular about what I put in it though. Sometimes I'd get flat spots or pinking with certain fuels. It wasn't necessarily the supermarket ones that it would run poor on either. Super generally made it happy. But with carbs and a distributer it didn't have an ecu to control everything, so a variation in fuel from what was in the tank when I set it up could make it a bit stroppy! LOL
It did have a stage 3 head, fast road cam and a weber carb with open ram pipes though, so wasn't exactly civilised!
In a modern car, unless it's been remapped to run on it, super will make very little difference for the extra cost. It could make it run a bit smoother i guess, but you won't really see any extra power that's worth it for the extra cost. If it was the same price I'd use it, but for the extra they charge, personally I just don't see the point. A V6 costs more than enough as it is!!
Also, I used to work for Tesco, and I'm sure I was told that Tesco petrol comes from Texaco. That was quite a few years ago now so they might have changed supplier, I don't know.
I've never noticed a difference between standard Tesco or Sainsbury's petrol, and say Shell, BP etc.
Before I upset anyone, that's just my experience in my own cars over the years!!