Personally I go for the bootable USB. Just a personal preference as you don't have Windows to mess things up.
I have used the windows flash a couple of times when trying to sort out issues (already booted into windows) and needed to do a bios flash back. It worked perfectly both times.
I'm so hoping that this bios update will sort out the two weeks of waiting that I have to endure whilst booting into windows 7 ;)
Out of interest, what was the issue with the sata optical drive?
Looking forward to giving it a go tonight. Fingers crossed.