The longest one day ride for me was about 450 miles. The longest total was 900 miles for round trip through Vietnam's Mekong Delta last year. Last month I went on a 800miles+ round trip from Ho Chi Minh City to the Vietnam/Cambodia border city of Ha Tien.
You can follow the trip here.
I'm planning a 1200miles round trip from Ho Chi Minh City to the city of Nha Trang, hopefully for next year. My dream trip would be riding from the south of Vietnam from Ho Chi Minh City to the north Vietnam city of Hanoi, which is a 1800miles round trip., some day.