6 sata or 2 sas?

Hi, I don't know what would be better in my situation. I have a HP pro desk 600 which has very limited connection (only 1 NVME and 1 SATA) and I'm looking to expand my storage.

I was looking at M.2 adapters and found out that SAS drives are full duplex. So would it be better if I had less SAS drives that can work all the time or more SATA drives with higher RAID?

Wich way would I run into throughput limits first?