Ditch the porter hard case, for many reasons. It's heavy, expensive, and it just scream "steal me!!!!". You can get similar protection without all the thick padding. From my experience (mostly Singapore Airline), they weight the obviously big carry on bag, so try not to make your carry on bag look very stuffed like it's going to burst and explode. In this case, something like a duffle bag would do, the duffle bag with rolling wheel could be hard to find though.
Long story short, this is what work for me:
Most of the time, they don't weight your laptop bag, so keep all the heavy stuffs like regulator (I have a $1500 regulator that I wouldn't feel comfortable check in), batteries, camera, tablet/laptop in your laptop bag. If there is more room in your laptop bag, stuff it with all the arms, clamp etc that can go into small nook and corner in your laptop bag and they can take all the abuse. The laptop bag will be carried on your shoulder weight is not an issue, you just can't run with it.
As for the overhead bag, get one of these to go into the duffle bag (remove the caddy tray of the toolbox):
The toolbox is use to keep your housing (make sure to not latch the housing), strobe, light and other delicate stuffs. I put my housing into a zip lock bag so there won't be any dirt to get on the o-ring. wrap everything with a microfiber napkin size tower to act as buffer so they don't scratch each other. The microfiber tower come in handy when you need to dry your gear when you're at the resort. The toolbox can act as double duty to bring onto the boat to keep your wallet, keys, sunglasses, defogger etc.
Anyway, stick the toolbox into the duffle bag along with some loose items like laptop charger, snack, magazine etc. In the case where the plane is too small and you have to gate check, the toolbox will protect your equipment, as long as they don't drop from a 5 ft height or have anything more than 50lb of stuff lay on top of it, the toolbox is adequate.
Some people use the photography's vest, which I haven't had the need to go that route. Gate check is not the end of the world. One time I got weight by Singapore Airline, they gate check my carry on so I just bring the laptop bag with me to my seats. After 13 hours of flight, we transit in Moscow, and I didn't have to carry my 40lb+ carry on to go through all the security scanning in Moscow, just me and my laptop bag.