What about Lufthansa? I heard some time that they were looking to the 764 mainly for services between California and Germany (I think it would be a very very very stupid decision, since they don't have either a single B767/777, and, on contrary, they have many A340 in operation and in order. And anyway, what could the B764 do that a A330 couldn't? But, I'm not LH chairman...). but I don't know if it's true or just another rumour.
I think that both planes will face difficulties on sales process: the B757-300 because it's not a flexible plane, since it's mainly concepted to charter opertations; the B767-400 because the difference between it and a B777-200 Market A is minimum, and the B777 takes the advantages of being more modern and having a modern family existant and in perspective (772ER, 773, 77Xs), in oposition to the 767 family that seems to disappear in a near future.
TP343, São Paulo, Brazil.