do 'supreme' or super fuels actually make a difference?

As above TB – if you’re using diesel, it will be better in any car. If you’re on petrol, your car has to be set up for it.

Your diesel will definitely feel smoother and nicer, for sure. You’re not imagining it 🙂

The cetane improver btw, 2-EHN has a characteristic smell, and the premium diesel stinks of it so they aren’t fibbing.