I have an in built fog sheild in my HJC. It is very good, they only last about two months though. I also wear glasses, it is such a pain in the but.OK, this morning it was only 21 F, but since I got some Tall thermal underwear the day before, I had to give it a try.
The cold didn't bother me at all on my commute. BUT, I could not keep my faceshield from fogging, even opening it up at every stoplight. Halfway to work I had to just keep it open all the way, and that was NOT pleasant.
So, no more riding at that temp until I get my new Scorpion EXO 1000, we'll see if its built-in antifog coating is any better.