So I was looking into getting winters as up here it gets pretty bad sometimes and MTs behave like hockey puks on ice. Problem is, was looking at minimum $1200 for a set of 4 33"s. Heard a lot about siping and grooving so ordered me an ideal tire groover with #3 blades. I'll post before and aft pics when I'm done and comment on if there's an improvement before and after siping.
From what I've heard, it helps a lot. Tire compound is obviously a factor in colder weather but when on a budget -

 

Siping will definitely help and the more edges you have, the more traction on ice or packed snow. Keep in mind that if you are driving on a good snow build up on top of ice, no tire will help as the tire will ride on top of the snow as it skids on the ice. Until your tire contacts a solid surface, you are not in total control.

 

Siping works great. I used siped tires in B.C. snow for several years.

The sipes will make it easier to damage the tread blocks when you off-road during the summer, though. Everything is a compromise.

 

Nothing is as good as a studded tire on ice. But given my options, I'd say its a good trade off. I don't plan on siping the outer blocks much to avoid chunking in the summer. Note taken however.

 

Why run 33"s in the winter? What about pricing some 255/75/17 or even cheaper 265/70/17's? I'm sure you'll see a much lower price point. Post some pics of your work though, curios to see how it turns out.

 

I ran 4 studded tires for years, then discovered hydrophyllic rubber - like what's used in the Blizzak tire. Never used studs again. The rubber is stickiest right at the temperature where ice is slickest (-1 to +1C). The tires also have lots of siping. When I couldn't afford two sets of tires I could run them all year and have studded performance without 2 sets of tires. Probably not something I'd run on a Jeep in summer, though.

In any case, siping is the best choice when your existing tires hafta get you through winter.