Posted this on another forum, maybe of interst here as well (for some at least):
Merino wool, 1 or 2 layers, as base layer and wind proof textile on top. A road textil jacket is fine (everyone have one of those laying around?), if really cold, with the thermal liner. The EDZ inner shell stuff (google it) is great for back up or if just very cold. Either pressure suit above base layer (actually adds a bit of warmth as well) or the integrated protectors in jacket.
Smartwool merino socks and wool soles
Gloves. Hard to get around a bit bulky ones. I've go some good gloves from HELD, they're warm and ok regarding bulk. Handguards help, heated grips too.
Fleece buff, keeping neck warm makes a big difference
But the biggest problem is misting. I have an mx helmet with visor, advantage being I can flip it up as soon as stop (that's when the problem starts ofte) and when I start riding, I keep it open for a few seconds to blow off whatever mist is there. Off course a road helmet would do the same (maybe with pin lock).
Also have Smith goggles with a small fan that also helps quite a bit.
What makes a big difference, is the breath box in the helmet leading breath down instead of up on goggles/visor. There are balaclavas doing some of the same. A mx helmet has a lot of ventilation in front so gets very cold at speed. If no breath box, I guess gaffa tape will help?
But hard to get rid of the misting and gets worse the colder/slower/higher activity (Unless you have a snowmobile helmet laying around). Keeping a spare pair of google could be a good idea.
Then there's always heated gear. Have that for below -10degC and low activity (forest roads). Even a vest will actually help feet/hand a lot since keeping core temperature up allows body to send more warm blood out.