Any 757-200 crossing the pond will probably have some sort of payload/fuel compromise taking place.
eg. With a dry operating mass of around 60T, theoretically you could get about 23.5T of payload on before you hit the MZFM of 83.5T, however the maximum amount of fuel you could then carry would be under 30T (typical MTOM of 113.4T) compared with the quoted fuel capacity of 34T or so...
Thomas Cook Airlines 757-200 service to Canada is a case in point, where their usual 235-seater config aircraft are reconfigured to a 185-seater config. Hence with a smaller payload, the maximum amount of fuel can be carried in order to operate the route without frequent tech. stops.