0-20: Saucony Drylete Balaclava. I wear this during a blizzard or during extreme cold temperatures. It protects the skin and prevents chapped lips. Keeping your head and face warm keeps your body warm. You lose a lot of heat through your head.
20-40: Saucony Drylete Skullcap. The skullcap is amazingly warm for how thin it is and I like to wear this in solid 30 degree temperatures.
30-40: Saucony Drylete Headband. This is also quite warm for how small it is, but usually better for anything above 30.
0-20: Saucony Run Mitt. This mitten is bulletproof against wind, and bitter cold temperatures. The mitten is your best friend when it is this cold. Your fingers are all in one unit so heat is transferred to each finger more efficiently than a glove. This is why even if you wear thick gloves, they won't work well, and hardly compare to this mitten.
20-40: Saucony Ulti Mitt. This is the 2 in 1 Glove/Mitt that I love because of how versatile it is. I like this because it is also very light and great to use during speed workouts. It is also good to use on windy days.
30-40: Saucony Nomad Glove. This glove is actually very good in cold rain. It is ideal for 30-40 degree temperatures. The Saucony Ultimate Touch-Tek Glove(not pictured) is usually a solid 40-49 degree lightweight glove, good to use in a race with slightly cooler conditions.
Disclaimer: I am not a medical doctor/licensed professional.