To go from Australia to Africa we booked a round the world ticket through the USA as it gave us a very large luggage allowance and we were going as volunteers for 2 years. I got the dimensions allowed and went and bought luggage that matched those dimensions.
I traved first on the same ticket, a month ahead of my partner and had no problem. When he went to check in he was told he was only allowed a standard 20kg bag. Our tickets were with Malaysian airlines but Qantas were handling the check in. He had to either pay the excess or leave the luggage behind. So he paid $3000 hoping it would be possible to sort it out later. But STA said the allowance was correct and it was Malaysian Airlines fault. Malaysian Airlines said there was nothing they could do.
I'm reporting this as a warning - GET IT IN WRITING. The luggage allowance often only shows up as a code on your ticket. It can be a very expensive mistake and if you arrive for a flight and they refuse to take your luggage you are in a very weak position.