20's certainly is a nice riding range, if it's dry. With wind and rain/ snow, temperatures feel much colder, so if it was a windy, blizzardy kind of night, it wouldn't appeal too much.
As long as there's no precipitation, IMO if I am already wearing a sweatshirt, there's no need for a coat too. Just cover all your skin and you'll be fine. I resist the temptation to wear shorts and give in the temptation for a balaclava and gloves.
Am I a big wuss for needing a balaclava for 30 degrees or less. I hate the feeling of freezing air on my neck, ears and that general area.