KBFI-PANC-RJAA
3.5 hrs and then 7.5 hours
With the load you are predicting, the 450 is going to make your trip far more bearable. With those legs you also have to consider taking food, lav capacity, aircraft redundancy for emergency planning, etc. The 450 has a full galley, lav system to suffice for 8 plus crew, range, systems redundancy to ensure no wet footprint, etc.