I went with the RPM non-Airgap, so that I could have great midrange and not have the engine take a longtime to warm up during a cold start.
A dual plane is mainly for low and midrange rpm power.
A single plane is mainly for midrange and high rpm power.
Since you plan to mainly have a street motor I would go with the dual plane, but to give you a good choice, we need to hear what you plan to use in the motor; i.e. compression, heads, cam, carb, etc.