Must admit that I get off the 777 after a flight feeling noticably more lethargic than after a flight on the 747-400 or 767....have suffered nosebleeds on 2 occasions (never before on 11 other a/c types) and very dry bloodshot eyes which I rarely get on the other a/c either. Many crew also have a whiff or 2 of O2 to try & alleviate symptoms...
Maybe these are just coincidences...but I have a feeling that 13.5hr LGW-EZE flights aren't going to be as popular when the route moves to 777 ops next summer.