Paul:
I would say hickory would be an excellent choice for the forearm (and buttplate) of a cue. Pretty much anywhere in the butt, with the proviso that the cuemaker balance the cue correctly, because remember -- hickory is VERY heavy (heavier than purpleheart, even though purpleheart scores very slightly higher on the Janka test). You might think about coring the cue with maple, and use hickory as a "shell" or jacket, because I think a solid piece would be just too heavy (and if used only in the forearm, would throw the balance point of the cue w-a-y far forward than expected).
Interesting side story about hickory:
We had two instances with storms ripping down trees in the last couple of years -- first, an F-1 tornado (rare in these parts), and then superstorm Sandy. During both, we had a couple hickory trees pulled down, and Lisa and I were out there for days cutting 'em up and splitting firewood. With the electricity out, hickory taught me how to quickly field-sharpen my chainsaws using a
Granberg jig. In all my years of woodsmanship (including being an apprentice for my Dad, who was an arborsman / tree surgeon on the side), I never had to do that before. I couldn't believe how resistant to cutting this wood is.
EDIT: Also, I was cutting one particular tree that was laying over a flowing stream (approximately 2 feet deep), and the pieces were going right to the bottom -- hickory sinks!
And then, splitting hickory is an experience. In an electric or engine splitter, at first, it looks like the blade isn't even penetrating the end of the log, and you hear the hydraulic pump start to strain. But then as the pressure ramps up, it lets go with a loud BANG. I mean, the log explodes! We learned quickly to not stand to the sides of the splitter, lest you get whacked with these really heavy (and sharp!) pieces that would definitely send you to the hospital. We couldn't believe how heavy this wood is, too. I was always brought up to believe that Oak was the hardest of the commonly-available hardwoods. That belief was shattered when I encountered hickory for the first time.
I can see why hickory is no longer used for baseball bats, because it's just too damn heavy. And, why we no longer have baseball players the caliber of Babe Ruth or Mickey Mantle -- swinging hickory like that tends to make you into a different player.
-Sean