M.2 to SAS or M.2 to PCIe adapter? and Why?

Hi, I’m in the middle of buying parts to upgrade to a new server I got (for free)!
ML350 G9
From ML 150 G6

Now I need to switch to SFF disks, which is not really a problem because most of them are 2.5-inch SSDs
But I need a new drive for the OS because what I’m using right now is SAS LFF

I have an NVMe m.2 SSD that I don’t use, and I want to use it for this.

The motherboard doesn’t have an M.2 connection
So I’m currently thinking about what to do

Buy a PCIe to M.2
Or buy an adapter from SAS to M.2?

Which would be better?

I have free PCIe slots but I don’t want to waste them all on drives (because I already have one that I’m adding that is PCIe) because I want to have room for GPUs and faster network cards.

How much will the NVMe performance decrease if I use an adapter to SAS?
And I probably will buy the 2 slots variant of the adapter (if it will be sas to pcie, don’t know yet…), so I will have more room to add a drive in the same space

Full disclosure, I originally tried to post this on Reddit, but I have a problem with my account, and it won’t let me post it in r/homelab, so I’m trying my luck here.