I see that Dell have released an updated BIOS version A10.
Good to see that my experience trying to upgrade to A9 hasn't been in vain – some of the fixes sound like they specifically address the problem I (and presumably others) had. eg.
- Prevent potential risk of BIOS crash during WIN-FLASH
- Disable USB device during WIN-FLASH.
- It will skip to flash un-used ME block during WIN-FLASH
I'm not going to be in any rush to install this update however – I've learned my lesson on messing with things that are essential for my work!