I researched the crap out of this subject and bored the readers of this forum to tears with my experience with my Edelbrock 750 #1407.
I've decided, FOR MY PARTICULAR APPLICATION, to go with a holley as well. Although the Q-jet gets good reviews as the "best all around carb for day to day drivability" it is not the preferred carb for medium to highly modified engines.
The other falicy is the only a particular CFM rating is applicable for a particular engine. I quote Gerard Forgnone ASE Certified Master Mechanic, Engineer and Inventor. "I took the 600cfm carb off my 390 truck and put it on my 4cyl Pinto. The jetting was right on! Then I took the 390CFM off the Pinto and put it on a 390 powered 62 T-bird. The mixture was right on."
Optimium performance depends not on CFM but on signal strenth and restrictions (or lack of them).
The 600CFM may run great on your car as long as you never wind it up past 4500 rpm. But beyond that you may be severely limiting your top end power. A 1000 CFM carb with vacum secondaries will only supply what the engine wants, for example 650 cfm. But a 600 CFM may not be able to supply this peak demand. This would be indicated by still having manifold vacum when you nail it.
In light of this you should get the largest carb CFM which still gives you adquate booster signal and therfor atomization of the fuel. Holleys are great carbs for tweaking to obtain this balance.
My advice is that if you have a bone stock 350 with 175 to 200 hp go with a 600cfm 4160 series, for approx 300 hp go to the 650 in the same series, above that use the 750.
For my engine I've just purchased the 780 series 4160-3310 with four corner idle adjustment and secondary metering block. I'm also going to install the K&N stub stack on it as well.
Buy one of the books on Holleys or carbs in general. Vizard's book "How to build horsepower Vol2" was a good all around intro.
