Is a 650 carb what I want?

I've got a built 340, 10.5:1, Edelbrock RPM High rise intake, X heads, 1 - 20-232-4 Comp Cams Camshaft (not sure on specs..), 727, 3.23 rear, which is just going to be used on the street. I'm not planning on racing it anytime soon. I need a carb recommendation. I've got a Holley 750 double pumper which I got for free. I rebuilt it with a non Holley rebuild kit, andddd now it leaks. Also, a check valve is torn, and it was pretty gummed up inside.
I am going to buy a new carb, and right now my parts store has a pretty good special on Holley carbs. Is a 750 too big for this motor?
The carb size calculation of CID x Max RPM / 3456 says I should be using a 600 CFM carb, which seems a little small, but I don't need to be running an oversized carb either.
Is a 650 too small? Or is that pretty much what I want? Also, do I want a double pumper? Or is that more a 4 speed application?