I second DGroves on this..... we have been running SSDs in our xw6400 and xw6600 SATA generation II workstations for years now. Huge improvement over hard drives.
My advice: get a used Intel 320 series off eBay. I have settled on the 300GB one for these workstations. but you also can find the 600GB ones used.
Use the Intle Toolbox software to manage and update firmware on these SSDs if needed. The workstations are built on SATA Gen II technology but for practical purposes you don't need SATA Gen III technology to have an excellent upgrade.
The xw4600 and ZX00 workstations are SATA II also, and the SATA III workstations show up in the ZX20 workstations.
These also run W10Pro64 fine.......