Alright, so I'm drinking an early sample of my beer and I'm ready to report preliminary results. I need to pick up a bottle of Pumking to try side by side with this beer, but I can give a quick update now. Remember, I brewed an imperialized version of my Samhain Pumpkin Ale recipe, not an attempted Pumking Clone, though I was using the extract to try to get that malty/"cap'n crunch"y character that Pumking has.
Anyway, what you guys are calling the graham cracker character and I'm calling "cap'n crunch" character is very similar between this beer and Pumking. I ended up going with 1/8 teaspoon of the McCormick Vanilla Butter and Nut extract, and for a corny keg, I think it is right on. Maybe slightly less than what Pumking has, but I like it at this level. My beer doesn't have the ginger flavor I got from Pumking this year, but that pie crusty flavor is right on. My kegerator is set at 40 degrees and upon serving, the pie crust character is lighter on the nose than Pumking. The flavor is right there though, and as it warms, the pie crusty aroma grows to almost the level of Pumking. My beer is very different from Pumking in other ways (more complex maltiness, more body, more pumpkin flavor, different spice profile, darker color), but when it comes to the pie crust character, this beer is very similar.
So if you want to brew a Pumking clone, my recommendation is to use a flavorsome US 2-row and enough crystal 60 to hit the right color. Aim for 8.5% or so ABV, add a little pumpkin to the mash, bitter low, ferment clean, add about a teaspoon of ginger at the end of the boil, and add 1/8 teaspoon of the vanilla butter and nut extract at packaging. That will probably be closer to the real Pumking than anything posted in here so far. Good luck!
EDIT: By the way, if any of you guys live near Durham, NC and want to try this beer, let me know. I know it's hard to believe some random dude on the internet (look at the recipe they came up with so far!), but if I can get someone to taste this, they'll be able to confirm my assertions. Alternatively, if any of you brew a beer and add 1/8 teaspoon of the vanilla butter and nut extract, please post your results so everyone can share in our discovery.