In my own experience all airlines treat carry on slightly different. At times I have been asked to weigh my carry on (and get it tagged) at check in, at other times (especially in Melbourne) when I have gone into passport control area. Other times it has never been checked - although one time they were checking size as we were boarding and those too big were asked to leave them to be checked in. This particularly happens on smaller connecting flights.
I have always slung a body and lens over my shoulder (and given the second body and lens to my wife if necessary). I have carried my laptop in either a second bag or once again just carried it through until I am at the gate. When I am inside the plane I put everything back in my carry on bag and stow it away. Now I only carry a lowepro 200 slingshot but it easily carries three lenses and a body.
Do not put anything valuable in your check on - apart from the chance of getting stolen your baggage could get lost. I speak from experience.