I also have an option 'CSM Support'. When 'Enabled' it allows configuration of three new options: "LAN PXE Boot Option ROM (Disabled/Enabled)", Storage Boot Option Control (Disabled/UEFI Only/Legacy ...
Even an old SSD like the BX100 will be faster. What's listed in Hard Drive BBS Priorities? What happens if you set Storage Boot Option Control to UEFI first? I don't really think either of those ...