I answered all of those questions in my above post....
The i7 2600k is going to be around 15% faster clock for clock, and will overclock higher, more easily.
It will not be that expensive, they already stated their pricing. It will cost around as much as a 1366 i7 does right now, give or take $20.
If you wait until January to buy your rig you would be foolish not to get Sandy Bridge, unless the current i7's drop quite a lot(which they very well might).