Correct me if I'm wrong, but the BA 763s are somewhat orphans, what being equipped with Rolls donks. The -524 something version, if memory serves me right. Also limited to M 0.79, and with a very high DOW, compared to GE and PW versions. I both sit and stand to be corrected.
And don't bank on them entering service with us; it's a crap aeroplane for integrators. Even UPS are quitely ditching theirs in favour of new build A300-600Fs. The 76 is too narrow, not enough volume, too heavy and too expensive to operate - when compared to the A300-600F. Yes, it can carry a lot of weight, but we usually run out of volume way before we reach the MZFW. As you probably know from flying the 75; it rarely happens that we reach max payload on intra-European flights, bur regularly run out of volume and have to dump freight. Enter the bean counters, who only looks at the underload, and then asks silly questions.
It's only bean counters who focuses on max "theoretical" payload - the guys and gals in operations are looking for volume first.
We are looking at the 762, again the issues are lack of volume and a high DOW compared to the A310. And you can get a converted A300-600 at around the same price as a 762. No contest, really.
Now this should spark a nice Boeing vs Airbus debate. Well, it has been a while hasn't it ?