I take your point DaveReidUK, Part of the problem Boeing has is deciding quite which segment of the market they are aiming at - range or load capacity. Given the expansion of the industry as a whole I incline to the view that the 767 would be the logical choice (if a choice has to be made).
Then again, a new design is going to be a compromise and maybe the reason why Boeing built the 757 and 767 in the first place was they decided a compromise wouldn't work.