What BIOS version is on the board now? The BIOS chip on the board should have a label with the factory BIOS version on it.
Can you use the F-Stream utility to OC in Windows? There is a beta version of F-Stream in the Beta download section, dated 7/30, which should be before the removal of Non-Z OC.
I wonder about only one BIOS version being available, as if earlier versions were removed. The current 1.50 does list Non-Z OC. I would download 1.50 now and just save it for possible use in the future. Any BIOS that has a "CPU code" or "microcode" update is NOT what you want.
It may be possible to find earlier versions of your board's BIOS, if that would help.