And I should add, now that the Amex BA Premium Plus companion voucher allows use on journeys commencing outside the UK, along with the lower £10k spend threshold, it seems preferable to spending $30k to earn the Chase equivalent.

A final consideration in choice of country for registering BAEC accounts is the taxes and fees quoted for avios redemption flights - in addition to being hard-coded in the currency of BAEC account-domicile, I find that the actual levels also vary, quite substantially in some cases between US or UK accounts, for the same flights. This might be a result of yet another BA IT bug, but I think equally likely that BA actively chooses to vary the amount of the T&F charge based on domicile.