Yeah, they were designed together, with the 767 coming out before the 757, but they were entered into service together. The 767, although bigger, is a smoother flyig airplane because with those big wings, you've got a lot more control surfaces. My Dad says that the 757-300 is it bit sketchy though, as its the length of a 767-300 that he flies a lot but you're going faster than any other airliner before V1 and you can go more than 35 degrees in pitch without hitting the tail skid (which he hasn't done). However, funny my Dad's favorite plane is the 767 but its the only plane he's had with Delta thats had an engine failure.