My feet stay fairly warm, so I have gotten away with riding in Sidi Dominators and mid-weight wool socks fairly far into the fall (down to near-freezing temps). The real problem, though, is going to be when it gets wet on the roads from either rain or snow melt. I'm sure shoe covers would help (some claim to be fairly waterproof), but a good pair of waterproof/windproof shoe covers cost enough (well over $50 in most cases) that I ended up just splurging on a pair of winter clipless shoes. Lake Cycling makes a few solid winter shoes, but they cost around $180 to above $200. They will definitely last for a few seasons, though.
Is this for commuting or training? If commuting, I think it is good to get a set of platforms and wear boots or sturdy shoes with wool socks on most cold winter days. Your feet are going to freeze in Sidis when you'll step in a puddle of slush and have freezing soggy feet. And you would lose a toe to frostbite if you had nothing over geniuses in -20 windchill.
If it's for training rides, you can still do many good winter rides in those shoes. If the ground is dry it should be no problem with ski socks. I have the specialized defroster shoes. They have some extra insulation and will keep your feet dry longer when the roads are slushy. They are good for a bike with no fenders when it's wet.
Unless it's a race, full fenders and regular shoes/warm socks on a bike with a bright headlight is all I ride in winter.