[Ben Jenssen]

I had a 3,1 mac pro for many years, and like Jack I put the SSDs on a pcie adapter card which was the biggest boost to the general feel of the mac that it'd ever had. Much better than the sata drive bays.

And about APFS; it's what you should use with ssds, and enable TRIM. It behaves a little differently from HFS+ in Disk Utilities, but the very main new thing that you will notice is that if you create a new partition, you don't give it a definite size! APFS will manage partitions on a drive and give it space as it needs it. Free space is shared between partitions (or volumes as they're known) to put it another way. Very nice.