Is there any benefit to using a square bore carb vs a spread bore. It would seem in theory at least that the square bore carb would give a more balanced charge especially considering the frequent wide open throttle position when used in boats. In automotive applications the Q-Jet shines for a variety of reasons but what about marine when economy is not the priority?

Main reasom I can see is that you have a larger selection of intake manifolds to choose from. Both are good carbs in their own right. Also there are very few aftermarket marinized spreadbore carbs to choose from.

Personally I'd pick a Demon

In all seriousness just changing a carburetor is not going to net you much in a marine application. Given the amount of HP it takes to make a noticeable speed difference. That being said if you're building, or modifying a performance engine then using a modular style carburetor that can be more precisely tuned would be recommended.

The Holley (demon etc), do have the advantage of dual fuel bowls. A Q-jet with the one bowl could technically get sucked dry if your fuel system wasn't up to snuff. Otherwise, you prob wouldn't notice a power gain...

I'm a Q-jet fan myself, but they make more sense on cars....