A good cfm for a leaf vacuum largely depends on the size of the leaves and the amount of leaves. For example, if you are dealing with a small volume of leaves, you might be able to get away with a lower cfm rating. However, if you have a lot of leaves, or large leaves, you will need a higher cfm rating in order to effectively vacuum them up. The best way to determine what is best for your needs is to experiment with different settings and see what works best for you.