Doomnova:
It's true that multiple factors besides gender bear on SAC rate, and some are modifiable in theory with lifestyle changes (I say in theory, because for some of us, that simply will not happen) or skill acquisition/refinement (which hopefully does happen over time).
It is also true that some people come out of basic OW class without fine tuned skills yet have very nice SAC rates & can stay down a long time on an 80 cf tank. I suspect that if we surveyed large numbers of the low vs. high SAC fresh OW students, assuming roughly similar skill sets (they won't quite be equal), that smaller & leaner will tend to have lower SAC. And women tend to have lower total body mass than men.
Some outliers will be the exceptions that prove the rule. There will be some fairly big guys with good SACs.
There will be some people who, through good fitness levels & dedicated skill acquisition/refinement, will drive their SAC down and do well with an 80 cf tank.
But at the end of the day, I think that on average big, chunky guys who get no closer to the gym than driving by it occasionally are often either going to dive larger tanks when available, or else plan their profiles around parameters other than a strict 'rule of 3'rds' policy. Assuming excellent conditions, such as Bonaire shore diving or in a quarry.
If you're diving the open ocean with a real risk of popping up hundreds of yards from the boat and they can't see your head for the waves, or some such, then gas conservatism will be different.
Richard.