I believe there is a 10,000 bonus for every 60,000 Marriott points transferred to United.Thanks @sudor for clarifying I wanted to see if there were any other options that wouldn't loose too much in conversion. And was also wondering about Aeroplane and Advantage.
Apologies for triple-checking, but this is all very new and rather confusing...
Hypothetically, if I wanted to end up with 103,500 United points I would need to use 302,400 Amex points. Yah?
AMEX (3:2) + 50% = Bonvoy (3:1) + 25% United
302,400 (201,600) 302,400 (100,800) 103,500
225,000 Amex to Marriott (with 50% bonus) = 225,000 Marriott Bonvoy points
60,000 Marriott = 30,000 United (60,000/3 + 10000 bonus)
225000 Marriott = 105,000 United (180,000/3 + 30,000 bonus + 45,000/3)
Considering 225000 Aus Amex points = 112,500 Airline points, so ending up with 105,000 United isn't too bad. Obviously only works with the Amex to Marriott transfer bonus though.