I've gotten 1.35it/s that corresponds to 38s, but I've the M1 Max with the 24 cores GPU (the "lower end" one).

I just set up a similar thing on my own a bit differently than OP did.

Apple M1 Max with 10-core CPU, 32-core GPU, 16-core Neural Engine - Takes 38 seconds as well up to 46 when it gets hotter.

Can anyone give comparison with Nvida gpu in terms of performance?