Freezer Question - Will foods and liquids freeze faster in a fully packed freezer vs. in an empty freezer? ?

The most important question is which one is colder. They're different freezers, they may not be at the same temperature. Use the colder one.

Next, you need clear air flow from the vents, so cold air gets in to the freezer compartment, and clear flow around the new item so heat is pulled away. If the full freezer is packed enough to reduce those air flows, use the other one.

Other than that, I don't know if there's a difference. Does fullness that doesn't block the vents hurt (more items that can emit heat) or help (those items may absorb some heat from the new item)? Is a dedicated freezer faster at cooling items than the freezer part of a refrigerator? Is the dedicated freezer 50 years old, were they slower back then?

Empty-that’s why I put the bodies in there, erm, I mean the food 

Take outsosme of the food in the top freezer. Freezers work as a giant ice cube when other items are already in it. 

A full freezer acts like a giant ice cube,and significantly helps freeze things faster than an empty one.Hopefully you have room for the pops !  🍧

Yes, but this will just depend on the freezer and the food stored there.

While the packed freezer will have more cold mass to exchange with the warmer pops, I'm betting that putting the pops in contact with the freezer shell in the garage  will end up with a quicker freeze. Why not do half the pops each way, and get a gold star at the next science fair?

No, they will freeze much slower. Use the one in the garage.

The freezer that's got more room for the cold air to circulate would freeze items quicker.

The fully packed one, obviously.