I am working on Dell Optiplex 755 Mini Tower (MT). I have upgraded it to Core 2 Quad Q6700 and 8 GB memory. The base board is Dell 0GM819. Tech Specs are here on page 5. The PCI Express x16 connector (SLOT1) is occupied by my NVIDIA GeForce GT 710. But it looks like I have PCI Express x1 connector (SLOT4) and two PCI connector (SLOT2 and 3) unused.
Which kind of SSD (M.2/PICe etc. as well as the brand name) should I buy and where should I put it?
As a last resort, I could put a 2.5" SATA SSD in a caddy but not sure if there are any other better options available.