The 5 MB EFI update should be available from the Mac App Store for all late 2013 Mac Pros and it can also be downloaded directly from Apple's Support site.Mac Pro EFI Firmware Update v2.0
This update is recommended for all Mac Pro (Late 2013) models.
This update improves system reliability during reboot, resolves an issue with memory self-test, and improves graphics power management when using Boot Camp.
Article Link: Apple Releases EFI Firmware Update 2.0 for 2013 Mac Pro