Maybe its just that it's dry in Colorado, but I've been riding down to about 16F without significant issue this year. I'd done this in the past, but it always involved multiple pairs of long underwear, and like, a million jackets.
Thanks to Johno, I got some of this Polypropylene stuff from the surplus store, and pretty much wear it all the time now.
You can find kids sizes for super cheap, currently @ 6' 180ish, Im wearing kids XL, a whole 15bucks at our local surplus.
I think they only have mediums left at that link, but little Ry fits into those, and he's taller than my shoulder. The things stretch like mad, and they're under your cool pants anyways.
I'm surviving with Polyprop. Shirt (tall sized, so I can tuck it in), pants. Carhardt pants, wool sweater, vinal jacket, snowboard gloves, regular socks, Smartwool snowboarding socks, and combat boots.
And full face, of course, because ice is a bitch.
But seriously, the only part of me that gets cold out there anymore is my toes, and I'm saving pennies to get some Polyprop. socks. Having to keep the full face open is kinda a drag, it fogs up a ton, but your breath keeps your face parts from compleatly freezing.
Best part is that I don't feel the need to strip down when I get to my destination, nobody knows I'm geared up for a moderate expidition, and it's designed to be active in, so it doesn't suffocate you.
It's good shit (and waterproof, portland/seatle). You should get some if you're gona keep riding, and haven't done so already.