To keep toes warm here are a number of tried and true tips.
1) Your cold weather shoes should be one size larger than your warm weather shoes (in particular, toe box must be roomy). If you like wooly socks, then perhaps consider going one and one half sizes larger. Consider getting a pair of winter cycling shoes. Summer shoes are designed to allow for air circulation, and winter shoes are not. I ride the Lake winter boots when it is about 0 deg C – down to around minus 10 deg C or so (add booties for colder). My Lakes are about one size bigger than my summer shoes, and I usually wear thin-ish wool socks with them. I have loads of toe-wiggle-room, and my feet stay quite warm.
2) You must get off and walk BEFORE you lose circulation. The goal is to keep circulation going – not attempt to regain circulation. Regaining circulation takes about ten times the effort of maintaining circulation (at least it feels that way). Get off at all red stop lights and many stop signs and walk around 20 steps… If you do this BEFORE your toes go numb, you will greatly extend happy toe time. If you are into cyclocross, this is a great way to keep your dismount/remount sharp.
3) Booties plus winter boots plus toe warmers are essential for particularly cold weather (your definition of particularly cold may differ from mine).
4) Cold calves lead to cold toes. Full length socks under your tights are a surprising boost to toe warmth…. This lesson I just recently learned, and my toes were extra happy this winter.