Thank for more replies guys. Now I feel more relaxed. Sounds like it's not as strict as I had imagined. I have decided I'm going to take backup body with me after all (what's the point of having it if I don't take it with me). Now the weight of my roller bag is 10~11kg.
And I forgot to mention about I'm traveling with 4 people, all in business class, and we are all in the same one booking. The other three's carry-ons are definitely under weight about half of limit. If they try cause some fuss about my roller bag, then do you think if I were to tell them I'm going to remove some items and put them in others' bags, they'll let us through without further trouble? Since accident can happen anytime, I don't want to put expensive lenses that each costs a few thousands in unprotected bag at any moment. I want them to remain in my protected roller bag all the time unless I really have to remove them.