I fly BOS-LHR reasonably regularly -- I think next week is the 7th time this year. I strongly prefer the day flights from Boston, which limits me to BA and AA. I strongly prefer BA, but this year have found the price differential in business class between BA and AA to be sufficiently large that I wouldn't be able to justify taking BA to my clients. I don't think that they check, but I do want to be a reasonably faithful steward of my clients' money. For next weeks flight, I had a choice between $6400 fully refundable on AA or about $9000 on BA, with restrictions. If the differential is small, I'll fly BA and there used to be no differential.

Have you noticed a big differential on other routes?