Just FYI, for 64bit BIOS updates, you need the Dell Flash Utility.
So I setup a CMD
\\nas\install\dell-bios\Flash64W.exe /b=\\nas\install\dell-bios\OptiPlex_3050_1.7.9.exe /f /s /p=Password /l=C:\dell-bios-update-1.7.9.txt
/b is the location of the flash file
/s is silent
/f is force restart
/l makes log file.
The Flash64W.exe is a Dell specific flash utility. Running this first with 64bit machines is required (as I found out the hard way of wasting bunch of time on this for nothing)
I read up more bout it here:
https://miketerrill.net/2017/01/31/first-look-dell-64-bit-flash-bios-utility/
Dell Flasher Utility is here:
http://www.dell.com/support/home/us/en/04/drivers/driversdetails?driverid=v5pjd
Hope this helps others out.