When you say 100 MP GFX is "looking pretty good", you are making a strong argument for the Max... 64 GB RAM requires the Max, and I can't imagine processing files from my GFX 100S without 64 GB.
The M1 Max comes in 24 and 32 GPU core varieties (there is no 16 core M1 Max), and I'm less sure about that choice. It's a rather small upgrade cost, compared to the (essential) 64 GB upgrade, and to the overall cost of the machine, so my inclination might be to go for the upgrade.
As for the memory bandwidth, I don't know how that will affect things. On CPU intensive tasks, even 200 GB/s is unprecedented (that's the memory bandwidth of a good-sized server - 8 channels of DDR 4 3200 on an EPYC or Xeon SP). 400 GB/S is unheard of on the CPU side - no single processor in standard production supports either 16 memory channels or DDR 4 6400 in an 8 channel configuration (there may be some single supercomputer chip that does). Desktop CPUs are mostly around 50 GB/S, with a few around 100.
The other side of the memory bandwidth question, though, is that 200-400 GB/S is relatively standard for high end GPUs, with a few even higher. On GPU intensive tasks, that's still good bandwidth (remember it's used by both CPU and GPU), but nothing extraordinary.