An RR techie told me once the RB211-524H that you get on the 767 was pushed to its absolute limit in order to power the aircraft.

If you consider that the GE CF6, the competitor engine, can power the much larger A330-300, that's hardly surprising.

In fact, RR took the Trent 700 core and retrofitted it to the -524G, making it -524G/T for the 747-400, I don't think they've done it for the 767 though.

And, in fact, Trent engines are in fact still RB211s....if you open them up they say RB-211-Trent-772 or something along those lines.

I'll leave now....