I've just posted a reply and it's been deleted???
I'll try again...
YES YES YES The guide states 3.6x which includes all the firmwares in the 3.6 range.
My console was 3.61 and downgraded fine. I've also done my mate's console on 3.66 so YES it works well.
Any questions I'll be able to answer them pretty quick now I've replaced my PC's psu