The loads on the 757s at any time during the year are normally well into the 200+ range, heck it wasn't that long ago that there way talk of getting a Titan 757 for the summer at NCL, although I have heard some of the -300 crews talking about the fact that they may well be doing some longer sectors with the -300s next year, EK77W is correct, if it is just a straight swap for two -800s then Jet2 will be loosing out on about 30 or so seats per flight.