I'm pretty sure they're all identical chips. No doubt there are clocking differences. But that may be automatic based on thermals and not actually represent a difference in the actual chip.

For the Apple TV, they can overclock since it’s plugged into the wall. They may do something similar here.

I'd imagine thermal throttling will be responsible for actual performance differences across devices (but this is just a guess)

Yes I'm waiting for the shop to open to find out if they can be configured - I bet not.

EDIT: the store does not let you configure anything but the RAM which is absurdly expensive.