I flew CX about 2 weeks ago SFO-HKG in Y. Had one slightly overweight checked suitcase (25kg) and 2 computer backpacks. The checkin agent mentioned the overweight suitcase but checked it w/o charge anyway. No problems with the backpacks. I saw quite a few people with huge rollaboards in the cabin.

I wouldn't worry too much about backpacks or other suitable cabin baggage.