Common knowledge dictates keeping the fats cool and the tools chilled. But when you are preparing more than 8X quantity, this poses some difficulties, or at least some stress. The ambient air, the size of home blenders and food processors--it’s all a mess.
I worked out an answer a week ago, so I'm posting it. But I would love to see a better answer.
Keep the fats as cold as possible before you start. Done right, it will more than compensate for the warmth of hands, blender/processor parts, and ambient temperature.
Having somewhat chilled your choice of fats, separate them into small, 1 inch sized pieces, working with copious flour to keep them from sticking to one another. Place this in the freezer overnight. This allows the blade to chew up even near-frozen bits. I haven’t noticed much degradation with this method, though I wouldn’t the leave fats in for much longer than that.
Mix your dry ingredients together.
Put the thoroughly chilled fats in a blender/mixer, leaving some room. Then, using only as much dry ingredients as necessary, pulse the fats until you have pearls slightly smaller than fish gravel. This works especially good for blenders where the ingredients tend to get stuck at the bottom. If you get the chance, stow the blended stuff in the freezer while you work with the next batch.
Once you have completed the blending en masse, you can add the rest of the dry ingredients. You should have a uniform texture to the whole mixture. Add water until the dough comes together with limited kneading. Wrap and return to fridge as soon as possible.
I always mix pie dough by hand. And... I don't chill anything until half-way through the process. Sacrilege, I know.
Adam and roux nailed it in their comments above, you absolutely want to work in batches: I've never gone over four crusts in one batch without finding the results a bit too tough from over-mixing.
I aim for about three good-sized crusts per batch, mixing flour, salt, and half the lard until well combined. Then I throw in the rest of the lard, mix roughly, and into the fridge or freezer it goes (which one depends on how much time I need to work on fillings or whatever), along with the water and vodka mix for later hydration. The next batch goes in when the first one comes out, to chill while I quickly work in the now-firm lard, add the cold liquid, mix briefly and return to the fridge (always the fridge) to let it rest and hydrate. So on and so forth...
Even if I have someone helping me, there's only so much dough that can be rolled (much less baked) at any given time, so I don't find this process terribly annoying, especially if I'm par-baking the crusts or using a filling that can be prepared in parallel with the dough. Once going, there's a new batch of dough ready every 20 minutes or so, which usually means I have several chilling while waiting to go in the oven.
A technique in sausage making, where the fat also has to be kept really cold, is to freeze the mixer parts for at least an hour before mixing.
Also sausage makers might grind into a bowl in an icebath; not sure how practical these methods are for pastry, but it can't hurt to know them, right?
