Intake manifold issue.

[purebred]

I have a 350 performance engine in my 65. When I bought it, it had a Holley 650 double pumper carb on it. I recently put a Edelbrock 600 cfm performer carb on it to try and get a couple more gallons out of it. I have a Weiand single plane intake, My question is should I go ahead and pay for a new performer dual plane manifold or am I just throwing money away? All in all it runs pretty good now butidle is not always smooth until it realy warms up, I have heard that single planes verses dual are a little different, should I pay the 150.00 or just stick with the Weiand? any input is greatly appreciated. Thanks