450 vs 600 CFM Holly carb?

The previous owner of my CC Mustang put a 600 CFM Automotive Holley Carb on it. I want to change to a marine carb for safety.

What would be the best choice for a 1973 Mustang (302 4 barrel, Waukesa)?

The boat has ample power. Would the Holley Marine 450 CFM carb give similar performance with slightly better gas consumption?? The current setup totally DRINKS gas (I know, that comes with the territory). I was thinking the Holley 450 CFM (Part #: 0-80364) or the Holly 600 CFM (Part #: 0-80551)

I thought I would ask the experts here at correctcraftfan.com!

Thanks.

Remmber the engine is nothing but a air pump, to turn more RPM larger CFM carbs are used. The formula will tell you that a 450 will do the job on a 302, giving you good acceration and mileage as Reid said.   
However the fact when you use a dual plane manifold a larger carburetor can be used. Reason being that only 1/2 of the carburetor is used for each bank. If you had a open plenumn manifold the carburetor useage would change, that all the air is used by all cylinders. Dual plane manifolds are used for more low end torque, however the newer dual planes are effective to 6500 RPM.
It get complicated, however bigger cams need more air to turn higher RPM.
On my 351 I use a 850 CFM but I turn 6400 RPM.

Bill, Single vs Dual plane intake on a ski boat? Everything I've got is dual, is yours? But I was wondering this: With just about any 302 to 351 in a 16-19 foot boat, you automatically have ample torque. So if you're attempting solely to add top speed, i.e., top end power, would a single plane not make a little more power at 4500-5500, and thus potentially turn the prop a little faster, or is 4500-5500 still not high enough to appreciate the single plane advantage. And I guess if at all this would apply more to a modified engine than a stock unit. Single plane intakes for the small Fords are sure easy to come by, so before I plop down the $100 for a used piece, let me know if you'd tried it or what you think.

-In search of the ever-illusive extra MPH.

I run a dual plane Wieand Stealth manifold, It's rated at 6500 RPM. I don't think a open plenuim would help, unless you are going for a mile record. Higher hp motors turning 8-10000 all use open.
Most cams in a boat are dual pattern and use dual plane manifolds.
One reason being that you are on and off the throttle and negoating turns that require torque. Remember up 5250 rpm torque is always the higher power, after that hp is the higher power. The ski tow boats don't go over that rpm so they are runing on torque, not HP, everybody worrys about HP and don't realize they are running on torque.