I had issues with keeping my feet warm as well. Winter cycling shoes and one pair of socks works well until below 40, then I had to double up on the socks. When the wind chill becomes a factor and/or the temp drops below 30, I throw on a pair of overshoes. I also found that spinning non-stop keeps the blood flowing and your toes from going numb, so resist the urge to coast for extended periods (especially going downhill!) and keep your cadence high. You may want to try winter specific cycling socks as well. This may not work for everyone but hopefully someone finds it helpful!