I have been using Liqui-Moly for more than 8 years in my car and I don't believe that if two oils have the same specification one oil can give more fuel efficiency than the other. Remember the purpose of oil is lubrication, so a 5W30 oil from Liquimoly or ZIC or Caltex or Shell should give similar results as far as fuel efficiency is concerned.
I think the reason why my car is fuel efficient is because, of my tires Yokohama ADVAN DB, previously I was using Yokohama AVS ES100. I got about a 10% increase in fuel efficiency just by changing the tires. The second reason is that my daily driving route has a lot of long straight roads, less traffic and very few signals.