Putting it on paper is important, but before you do that, decide what type of pattern fills your anticipated needs. There are shell/gun combinations that produce beautiful, tight patterns where you might want a much more open pattern. Some of the tight shooters, you might as well be using slugs.
It has been my experience that if the Buck is stacked three/layer (common configuration), then the more open chokes, no tighter than Modified, produce even patterns. If it is stacked by twos, it most generally likes tighter chokes.