I am used to travel with my photo gear as follows:
1 Loewepro Vortex 300 Photo backpack as carry-on containing:
Weight is 18-20 Kilos
as checked baggage inside a torn suitcase containing:Weight 23-30 Kilos
triplecheck that your flights allow more than 8 kilo carry-on as here in Europe 8 kilo and less than IATA carry-on size limit becomes more and more normal
Basically you are prepared to pay a lot of money for extra baggage
As you wrote it's normal that the maximum carry-on weight allowed is 5/8 kg here in Europe.
The worst company is Blue Panorama in Egypt: 5 kg carry on and 15 kg checked. you cannot buy extra weight in advance.