I travel from Spain, via LHR (and BA) to PEK, my company also has a Y ticket policy. Yes the BA flights are busy however, I have had no problems upgrading the tickets in LHR and PEK to W, which makes a more comfortable trip (GBP 209 each way). I have also used AY, but I find them more expensive than BA, particulary when flying from Spain; comfort wise I cannot advise in Y, as my flight to Chongqing was cancelled and I was upgraded to J for the leg to PEK.

BTW I am a little surprised to note that BA PEK will be downgraded from a 744 to 77E this winter;