Wow, that's cold. Rode in -5 today which caused glasses to fog up with the visor down. The visor itself is a snow version and had no issues.
Yeah it was cold. I wouldn't do that again, but am glad I tried it out. I was teaching at a local college a the time and went indoors to teach my 3hr class and when I came out the bike barely started up. I hadn't thought about that in advance.
Not too long after that, I was riding into work one morning around 7am when it was about -10 out. And while I was merging onto the highway (westbound Gardiner from Jameson) the lead vehicle came to a full stop in the merge lane and so it forced the three other vehicles in front of me to come to a full stop. I was checking my blindspot while preparing to merge and when I looked in front I had to immediately slam the brakes and it lightly hit the classic pickup truck in front. No damage to the truck but the bike was written off, since all the front plastics were damaged and the bike had 90k on by then. But insurance paid me $8k for the bike and that was enough to buy a brand new DL650 - this made no sense to me, but I didn't complain.
On a separate cold ride when it was late at night and dark and foggy back in 2008, I was running full heated gear and my fog lights. Didn't have a voltmeter and drained the battery while riding. If you choose to ride with heated gear, some sort of voltmeter is a good idea and I've ridden with one ever since.