4 hole or open?
Generally a 4 holer will help your low end torque and an open spacer will help the top end.
I have a 4 holer 1" under my Edelbrock and it did make a better low end , and I can feel a loss at higher rpm's.
It's said that the optimum spacer can only be found by experimentation because each engine is different.
Regardless of which type you choose, a phenolic material spacer is better because it helps keep the carb cool.