Improve performance on ZFS SATA SSD pool?

I recently converted my main PC (Windows) to ProxMox but I was also having issues with this array when I had it as a windows storage space. I originally though it was an issue related to that, but I'm having similar performance issues (I had other reasons to move to ProxMox I just finally had time over the holiday).

I have it set up now as a z2 with one vdev of 5x 4TB SATA SSDs The performance currently is (MB/s):

Reads:

6087.69

1468.55

473.88

48.36

Writes:

2785.15

122.44

0.04

0.04

The last two are not typos, during pretty much any heavy write the whole system locks up even though the OS is on a different drive and pool.

Now part of the reason for this I think is I made a mistake a few months ago getting BX500 drives when I was thinking of getting MX500 drives. Simply put most of the drives in the pool are not great.

The question I have here, is this something adding some NVMe to the pool (a SLOG vdev would be my understanding, this is the first time I'm actually doing zfs) or would I be better off replacing the drives with better ones? Getting a single NVMe would be the cheapest option, but a few if I need to put multiple in the vdev would probably make it close to the cost of replacing the drives (not counting the possibility of selling the used drives).