Having flown LHR-PEK in whY, it was surprisingly tolerable. And direct flights, especially on a busy schedule, are worth a hefty premium imo. Unless this is likely to be the OP's only possible chance to sample CX F, I would pass.

I've only ever flown old F on BA: the food was terrible, the AVOD non-existent, the service was OK to good, but the seat was still v. good, despite being dated. On an overnight flight, that's what counts the most.

tb