How do I add a new SSD to an old mainboard?

My knowledge of this stuff is out of date, and judging from the research in the Qs here, I've missed a lot.

I have an older Gigabyte mobo with PCIe3 slots, but not M.2-capable ones. One PCIEx8 slot is free. I also have a free SATA3 connection.

I know what performance I can expect from a SATA connection, but I'm unclear whether there's any advantage to using an adapter in one of the PCIe slots to mount a new NVMe SSD. I understand (I think) that I can't get the full performance I'd get from a native M.2 slot. But can I still do better that straight SATA using such a configuration?

This won't be a boot drive, just storage. It will replace a RAID10 set of 4 5400rpm drives that use a H/W RAID controller.

I do not think there is a huge operating difference between SATA and NVMe. I have a ThinkCentre desktop with straight SATA Samsung SSD drives and an i5 CPU. I have a ThinkPad laptop with NVMe Samsung SSD drive and an 17 CPU. Both have 16 GB of memory. The X1 is faster but maybe 10% faster.

So I would stick with the straight SATA adapter (to economize).

You will notice a very large speed improvement in data access and operations over 5,400 rpm drives for sure. I got a big improvement from 7,200 rpm drives in the desktop.