I used a M2 Ultra 64GB RAM and 1TB drive for two weeks, which I decided to return. I did some research into forums related to disks and if you choose one 1TB or more, a different chip will be installed, allowing you to double the speed. That will not happen with 512GB, the speed will be half, compared to 1TB or more internal.
I decided to wait for the M3 release and I will purchase it with 4TB of internal storage, which consists of two 2TB internal modules. I cannot find the original post where all the technical details were provided, unfortunately.
I'm using a Trebleet TB4 enclosure, with a Samsung EVO Pro. It maxes out the TB supported speeds, see
post details.