The difference between an A and G rated tyre for economy is about 5% - maybe not a lot on 40mpg average, but over 20k miles (ca life of a set of tyres if rotated fr to back as they wear) then thats £180 saving in fuel.
You will find very few tyres int hat size with good economy ratings, the bulk of sport oriented tyres are E-G rated. The Goodyear Efficient Grip and Pirelli P7 blue are a couple of exceptions, there may be others. I ran Pirelli P7 cinturato (but not blue version) on my Mk6 Golf and found them very good tyres, not the sportiest out there but they handled some hard cornering in my hands without complaint although a lot of my driving is dual carriageway.
You also have to be careful when comparing tyres - the ContiSport Contact 5 has very different eceonomy ratings whether its MO (Mercedes), AO (Audi) or generic variants - MO is rated C for economy, AO E and the generic F rated !. Ditto Dunlop Sport Maxx RT - one varant is C rated, the other E rated !