IIRC there is a CSM Auto/Enable/Disable setting in the MIVE-Z BIOS but is hidden and probably a high chance that it does not work out of the box any way. With my P67 the RST page could be had by using the right or left arrow to tab through the main tabs as a default tab was not present for RST. FYI AFAIK Asrock has only just started adding RST tabs so still quite a few Asrock BIOS have the EFI RAID driver but no access to the EFI RAID setup utility in the BIOS.
What are you hoping for performance wise, a faster BIOS post time but with a possibly slower OS driver? 11.2 OS driver is still the fastest for me but for some reason does not work when using it with the BIOS EFI driver, not that I gave much time to testing.
With my own setup the ASUS P67 uses just a 4MB BIOS chip which is too small really. For instance it use to have a dual boot block for crash free operation, if something went bad when flashing one of the boot blocks the other could be utilized for recovery. Now there is only one boot block in order to make room for the newer stuff, very tight.