IMo, skip the Edelbrock Performer with the weighted secondary air door and make a better choice with the AVS style carb from Edelbrock and there Performer manifold. The AVS will operate smoother and the Performer performs like a stock intake. The 650 Thunder has a simar cfm rating as the factory carb @ 630cfm.
The RPM has a higher rpm operating range.
If you choose a Holley, 650cfm is fine. A standard VS is fine.