Well there are 32-core 2U rack mounts, so I'd guess you could put 64 cores in a 4U rack space. However, it will need dedicated AC, a LOT of air flow, and would probably have a sound rating of 88-90dB. Plus it will need two-phase power and special wiring. Definitely need that in a room far away and no chance to put it on a cart and wheel it around, unless you have two-phase power outlets all around.
The 24-Core (2x12-Core Mac Pros) would run without dedicated AC cooling with enough natural air exchange. And would have a sound rating of about 40dB. In other words, you can rack mount them and put them right next to you. Plus, a simple surge protector with a good old standard wall plug is all you need. Bring it to a shoot, roll it in a roller board, plug it in an go. Pretty darn functional to me....