I think we should clear up any misconceptions regarding cfm ratings and engine needs in this post. One of the questions I hear often is what is the best for performance, double pumper or vacuum secondary. Almost without exception this can be answered by saying double pumper, in almost every situation the extra fuel delivered by a double pumper will assist the engine during torque demand by keeping the A/F mixture at 11:1 or richer for longer periods than a vacuum secondary carb could. Of course a vacuum secondary carb will not need the extra fuel due to the restricted airflow from the closed rear secondaries.
Do you need the extra airflow afforded by a double pumper carb? The answer is yes if you are looking for the ultimate in performance and torque production, a double pumper carb will always outperform a vacuum secondary carb on the dyno during sudden throttle angle changes. The problem is that it is possible to stall an engine with to much air and fuel at once and backfire through the carb, this is the principle reason why it is always recommended to run a vacuum secondary carb on the street. My question to you is are you smart enough to keep some restraint and not floor the accelerator when the engine is under heavy load at low rpm so you will not stall the engine? If the answer is yes than you are ready. This is why manual transmission cars usually have double pumper carbs from the factory and automatics usually came with vacuum secondary carbs. The manual trans operator has more control over engine rpm than an automatic driver has.
To the average idiot consumer this is a wise thing to do, but the average hot rodder is smart enough to know better. As for cfm ratings you can run as big as you want but at some point the restriction reduction caused by going bigger will not offer any performance increase and it will be a waste. You could conceivably run a 1150 cfm carb on a 305 as long as you could stand having to be careful with how much throttle you give it under load and low rpm. I have run 850 DP Holley carbs on 302 Fords with no problems and only had to be careful how I drove it, a full throttle stomp at a green light will leave you standing there looking like an idiot.
If I had a choice on carbs to run on the street I would have to say a 750cfm Holley double pumper is all the carb you will ever need unless you have one very radical big block, and then I would recommend an 850 DP for up to 600 HP. A Dominator looks nice and can be driven properly as long as the operator is aware of the limitations. On the other side of the coin a 600 vacuum secondary will offer you 90% of the performance without exacting the toll of watching how you play with the throttle. Ultimately it is up to you, if you don't mind learning to drive a car with a careful right foot then a double pumper is right for you. If you just want to stomp and steer it, then a vacuum secondary carb is for you.
The trade off is to get the extra 10% of torque from the engine you need to make a driveability sacrifice with a DP carb and learn to drive it. Is it worth it? that's up to you.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo