@Musical Chairs
I do not think there is a board check at all.
In order to install El Capitan on my X58A-UD7 I had to change from Chimera to Clover as the boot loader. I added the SMBIOS for a 4,1 and my DSDT to Clover (mounted in root, not the ESP).
The App Store refused to allow the Si3rra download with a 4,1 SMBIOS, so I copied the config.plist to have a record of it, edited the one in the Clover folder for a Mac Pro5,1 SMBIOS and downloaded Sierra and created the UniBeast USB installer with my DSDT and the 5,1 config.plist.
I tested the new UniBeast USB installer using Mac Pro 5,1 in the config.plist on my X58A-UD7 doing a clean install on a separate drive and installed Clover to the new install. I forgot the config.plist on the desktop of the old drove was 4,1 SysDef and copied it into the new Clover folder along with my DSDT and rebooted from the desktop.
Sierra booted with the old 4,1 SysDef without any problem.
This is what I wanted to verify with other X58 owners - that it worked for others also and was not just a fluke on my hardware.