if your asking this question I kinda wonder if you should be out in double overhead surf. Thats some serious water moving around.
I beg to differ i still ask questions to myself about what board i should take in Big conditions its one of the issues/joys of having a larger quiver.
In answer to original poster - it really depends on the shape of the wave. No doubt DOH any shape is powerfull and a lot to deal with. But are we talking about 12ft style wedge waves? 12ft thick reef? 12ft closeout beachbreak? or punchy 12ft tubing reef? - - - its unlikely i would take out the same board in those different conditions.
It also goes down to personal preference :example: i have seen footage of guys ripping up tehupoo on quad fin set-ups it obviously works for them.
Its not just fin set-ups but the whole board set-up that makes the difference e.g tail shapes, rocker profile, thickness etc etc... in other words its not impossible to surf a retro fish in giant waves but its probably wholley unsuitable.
The best way to find out is to experiment a classic example is on one of the biggest days i have surfed (16ft+) i was on a 6'8 swallow tail shortboard and it preformed fine. I have also taken a quad set-up in super hollow crunchy waves and preformed just fine. Its up to you to make your own judgement on what works for you
Oh in larger surf you really want something has a fair bit of paddle power. The last thing you want to be is under gunned otherwise you are not gonna beable to paddle into a wave and if you do you will be taking off really really late. Having a board that is too squirlly in the tail is probably not a great idea either. Of course you should be comfortable with the board