What boots do you use ?
 

Just curious as to what boots you use against these frigid temps to protect the toes.

I wear my normal road shoes with neoprene shoe covers.
Duct tape is used to cover the webbing in my shoes.
The insoles are out of my shoes so that I can wear a thick pair of wool socks or a thin pair of nylon socks with a thin pair of wool over top.
When using clipless pedals my options are fairly limited. Either do what I am doing now or spend more money on a pair of winter riding shoes that don't look any warmer than what I have.

And how far down the temperature scale do you do that in?

I have been out at -15C. Funny thing is that when I ride my winter bike my toes are cold in about an hour.
When riding my road bike it is usually dry but colder and my feet stay warmer longer.
Winter bike I use MTB shoes and clipless pedals.
My road bikes have Speedplay pedals and road shoes.

My toes determine ride time. I pedal out into the wind and when my toes get too cold, I turn around and come home. Most times I just do a loop of 20-50Kms.