Your last sentence is most likely one of the things to look at Pauly.
Firstly I do totally agree with extra length for bigger waves .
Having the right board in bigger waves is only a small piece of the puzzle . The volume distribution as discussed already in this thread will definitely help with paddling however in bigger surf the, biggest obstacle 90% of surfers deal with the most is
CONFIDENCE and
FITNESS .
I am BIG into my fitness , and train specifically for surfing . I also eat well and one thing I can be sure of is that if your body is fit , and you are eating well then your brain is also fit and functioning your muscles at a higher performance. Your brain rapid fires responses to your muscles and body so fast surfing becomes automatic and you dont even have to think about it - It just happens
This then transforms into confidence and
CHARGING.
Here's my point of view . Once Im on my feet I want the best piece of performance equipment under me . I don't want to be having to "nurse" a board through turns because I need that extra volume for paddling. Some people will disagree with me on this and share a different perspective.
While my body is still young enough to be fully mobile , I want to make the most of these years and rip for as hard and long as I can. My fitness is the key to making this happen.
Plenty of time for me to cruise on a Mal later on in life
I think you should be riding a 6'3 with around 30 litres of volume for your shortboard , then a 6'5-6'7 with about 32 litres for your step up.
Im 36 and have an extra 10 kgs on you mate and ride similar dimensions without an issue .
Let me know when we are going board shopping