A flight from Auckland to Honolulu with the mentioned stops Fiji and Samoa is (for me) not an issue. If I have my maths correct, the longest stretch is the last one which is approximately 2242 nm. However, in between lies Kiribati (6900ft runway) and Kona (11000ft runway). The longest overwater stretch between possible diversion airports is Kiribati -Kona which is approximately 1678nm. Whether it's a B777 or a B737 makes no difference to me.