I am extremely cantankerous and simply refuse to hump any bag around that weighs more than 18kgs. A 25kg suitcase is a serious lump of mass. Baggage handlers don't like those sort of weights and it's amazing how often bags of that weight get damaged or have their handles broken off. If you must travel like a circus elephant then pay the extra and spilt your weight into three bags. That way you'll at least have room to buy some casual trinkets or gold bars en route.