WCCFTech got them from VideoCardz.com, the originator of the leak.
Turbo Boost Max 3.0 allows the user to choose a core to clock at much higher speeds than regular old Turbo Boost 2.0. This feature was code-named MSR-1999 and has been discussed for a while in enthusiast circles :-) I think it requires OS/software support, though, unlike Turbo Boost 2.0.
Anyway, a 15% boost on the 6950X would put it at ~4GHz on a single core.
The $1723 part is the triple cheeseburger to allow more folks to justify to themselves buying the $1089 SKU as being reasonable. :-D
As an Intel shareholder I hope they sell a lot of them, even the $1723 part. As a desktop PC enthusiast I wonder who in their right mind would pay so damn much for an outdated microarchitecture in a 140W device no matter how many cores it has. In fact I wouldn't buy a 140W desktop MPU for any price no matter how many cores.
If I wanted more than a quad core mainstream then I would look at a Xeon based workstation. At least then you get ECC memory.