Raspberry PI5 NVME - PCIe gen config

Initial situation ‘only’ 600MB

So I had installed HA via bootloader and imported my backup. So Internet installation directly on the PI.

I then executed this command:
dd if=/dev/zero of=/mnt/data/temp.img bs=8k count=256k

Result:
➜ ~ dd if=/dev/zero of=/mnt/temp.img bs=8k count=256k
262144+0 records in
262144+0 records out
2147483648 bytes (2.0GB) copied, 3.323903 seconds, 616.1MB

NVME PI shield nvme: Pimoroni PIM699
SSD: Crucial P3 Plus M.2 500GB

Info from pimoroni:
The Raspberry Pi 5 will run at PCIe 3.0 x 1 speeds at best, even though this mode is unsupported officially, so most drives are limited to around 700-800MB/s read and 350-450MB write at peak.