I heard there are cold-weather specific cycling shoes out there, but what makes/models have folks here actually used? I'm wearing a cheapy pair of Giros right now. Like 'em, but even with thick socks, I still need some insulation.

BTW- I commute 11 months out of the year. With platforms I wear a pair of insulated Columbia hiking shoes. But riding fixed... need retention.

I have a pair of gore thermal shoe covers that I use from around 40-55°F. I have a pair of diadora polaris 2's that I got from the closeout bin a couple of years ago. I got them a size too big, and they are comfortable with heavy socks down to about 20°F, maybe a little colder. Below that I wear boots with platform pedals. I don't ride my fixed-gear when it's below freezing.

When it gets really cold, I run bmx style pedals and use my winter boots.

45nrth stuff is nice.

I have these from Lake, I like them a lot.

You're in Pennsylvania, right?
Find yourself some hunting socks...battery powered electric hunting socks.
Feet in the socks, socks in the shoes, neoprene shoe covers over the shoes.
You will be good to go.

Specialized Defroster boots. These are not cheap. They do work well in temps all the way down to 0 (tested this past winter) and they are waterproof (tested walking home, pushing my 35 lb fat bike through a foot of snow.

Why not use straps on the platforms you already have and use the boots you already have?

I've been using these:
Amazon.com: Planet Bike Comet Shoe Covers
And they're pretty great. I wear a size 11 and had to get them in XXL.

I too have used several pairs of Lake winter boots. Those and some badass wool socks. Once it starts to get 30 below tho I do go boots & flats.