Good question. Beyond my capability of answering in terms of sheer size. It's definently been proven the bigger the fan, the greater the thrust (usually). I don't know for sure if the 744ER just has more powerful engines or has the GE
engines for the standard 747-400. (GE
engines have to be the most powerful available on the 744, or else they would not be the only engines offered for the 744ER). I don't know always if an engine has to just be slightly modified or increased in size to generate a slight difference in thrust (say, 2,000 lbs. more per engine). I'm not sure if size plays a gigantic factor in this role. I also do not know the thrust of the GE
engines on the 744ER, which makes it even more difficult for me to answer this.