Well, after much consternation and consideration, the wife and I decided to go with a 12-ounce popper. The model we ordered is the Great Northern TopStar:
That model was being sold by Costco.com for $279.99 shipped (plus tax). Unfortunately, Costco doesn't have it in stock anymore. It was $20 more through Amazon.
As mentioned above, we've been using seven to eight 4-ounce pre-packs per evening showing at the Booth Bijou Garage Theater. Assuming 8 cups of popped corn per 4-ounce pre-pack, that's roughly 60 cups of popcorn. Two 12-ounce batches in the big popper would produce 48 cups of popcorn. And according to one reviewer on Amazon, the 12-ounce machine's bin actually holds 64 cups. So, two 12-ounce pre-packs and one 8-ounce pre-pack should work perfectly.
I've read reviews on this machine on multiple sites (including Costco's site before it went out of stock). There's one negative review on Amazon but, by far, the vast majority of the user reviews are 4-5 star. I also found an older model (different cabinet graphics) that Amazon used to sell and it had six 5-star reviews.
I really wanted to buy an American popper (Paragon or Gold Medal) but I also really need at least a 12-ounce machine. A 12-ounce machine from an American company is more than a thousand dollars. Ouch!
I'll report back with my thoughts once I've had a chance to use the machine.