As people stated in the announcement post, a high memory bandwidth doesn't really benefit CPUs much. That's also why AMD and Intel don't have high memory bandwidth on their cores, because it doesn't really help performance.
Where it is beneficial is the GPU; for comparison AMD and Nvidia cards often exceed 400GB/s. A desktop RTX 3090 has 900GB/s.
This turned out to be correct, look at https://www.anandtech.com/show/17024/apple-m1-max-performanc... -- the "sustained" measurement is on the right hand side of the graph. It hits 243GB/s bandwidth with 8+2 threads, 224 with just the 8 performance cores.
Where it is beneficial is the GPU; for comparison AMD and Nvidia cards often exceed 400GB/s. A desktop RTX 3090 has 900GB/s.