P&W v Rolls Royce on 757
Which is the most efficient engine fitted to the 757: the Pratt & Whitney or the Rolls Royce? I always assumed it was the Rolls Royce engine but I read some data yesterday (admittedly published by P & W) that on a Frankfurt - New york sector you can carry an extra 55 pax or over 5 tonnes of freight more than a Rolls Royce engined aircraft. If the P & W engine is more efficient why have more customers chosen the Rolls Royce engine? Can anyone enlighten me?