Depends on how you pack and what you pack.

We did 45 days on a Circle Pacific type trip (7 countries 11 cities) on that 7kgs carry-ons for each of us. I lost 2 light jackets by accident, not by design. Because after NZ and Australia, we went to very hot SE Asia and the jackets got left at the plane and then at the hotel. Also lost a pair of shorts in Hokkaido by accident again. We still have enough to meet our needs. We did some laundries of jeans and such, in Hong Kong and Taipei. We hand-washed undies in hotel rooms. When you go on a trip this long, there is no way to avoid washing on the road, so you might as well pack much lighter.

We also did a 16 days Transatlantic cruise followed by 15 days in Europe on a 10 and 11kgs carry-ons, which contained formal clothes, i.e. suits and evening gowns, with the shoes to go with.