Vacume secondary spring.

[G_Edmonds]

Since you are getting the quick change kit, you can try every spring without too much trouble. Dynos are about wide open throttle. Vacuum secondaries are more about the transition between part throttle and full throttle. The lightest spring is seldom the answer. It just opens the secondaries right away and bogs the motor without the extra fuel that a double pumper would add. Also, what seems the best/fastest is not always the best/fastest as judged by seat of the pants. In other words, make small changes to see what really works.