Above my pay grade! You probably operating with a fixed speed on M1 so you can't intentionally cripple it, but it would be interesting to see "What would this look like if Apple had paired it with standard DDR4-3200?". AMD's Zen core's are known to respond well to lower latency RAM, but in the PC space you're not getting anything close to what Apple has with the LPDDR4x on package. You could try benchmarking the Intel and Ryzen chips with DDR4 5000 and try carefully tuning the memory frequency and timing to find the right balance of bandwidth and latency.

this is a reasonable test: https://www.cs.virginia.edu/stream/ref.html

but it's pretty straightforward to just copy giant buffers in order/out of order and squint really hard at the results