Mark,

I am not sure really how to do it without loosing the array.

The safest way would be to:

1. Uninstall Intel RST in windows
2. Restart the system and boot into a Acronis or similar program to backup the raid. (Don't go back into windows)
3. Flash the BIOS with older ROM if you want. It shouldn't matter if the ROM stays at 11.5
4. Delete the raid in bios and make it again
5. Restore the backup and boot windows
6. Install older Intel RST and setup cache options etc.

Someone else might have a better way.