I've just booked a DONE4 and thought hard about where to credit the points. I originally thought Matt's idea best but as AY requires 80k for Emerald vs BA Gold at 20k. Best earning rates away from the host airline is going to be, for BA, 50% (EI, AY, JL, QR etc) so 40k miles needed (hiding fare from AA/BA by using codeshares on their legs). Best rate on Finnair is 250% on the "FAIB4" so 32k miles needed.

The big rub was carrier fuel surcharges. On BA vs JL or QR, I saw surcharges of £200-£300 more per sector choosing FAIB4 metal which soon adds up on the 16 sector DONE4 I just purchased. As an example, I'm flying JFK-LAX on AA but JL flight number and MSY-LHR on BA with AY flight number so will earn 50% miles rather than fare based that the airline would see if I used their own flight number.

I needed to add two more separate trips to obtain the itinerary I wanted (CHC-AKL-NAN and LHR-FCO-LHR side trip) and get a top up of NTPs with BA's current offer. Altogether, the RTW plus attachments has me earning 21k NTPs on BA for 34.7 UK pence per NTP. Plus the holiday of a lifetime in decent seats.

BA's TP Offer (per sector)

Euro Traveller - 75 bonus tier points
Club Europe - 175 bonus tier points
World Traveller - 150 bonus tier points
World Traveller Plus - 275 bonus tier points
Club World - 400 bonus tier points
First - 550 bonus tier points

https://www.britishairways.com/conte...er-point-bonus

https://www.britishairways.com/conte...points/flights