Edelbrock AVS2 Carb Dilemma

I am looking to purchase one of the new Edelbrock AVS2 Carbs. I am trying to decide the best CFM Rating for my application. The 1901 - 500 CFM or the 1906 - 650 CFM.
I Have a Duster 1973 318, Stock heads, Edelbrock LD4B Intake, Comp Cams High Energy 268H, Stock exhaust manifolds, Dual exhaust with Turbo style mufflers, 833 Overdrive 4 speed, with factory 2.94 rear gear. The Car is a weekend cruiser just for driving fun with the occasional romp to 5500 rpm. I do not want to over Carb, but I don't want choke the engine down either. I am looking for the groups thoughts and experience.
Thanks for the Help.