The quad-core i7 875K is based on Intel's 45nm Lynnfield core. It works at 2.93GHz, can process eight simultaneous threads with Hyper-Threading, features 8MB of L3 cache and has a 95W TDP. Meanwhile, the Core i5 655K is based on Intel's 32nm Clarkdale core with integrated graphics. The dual-core processor can handle four simultaneous threads using Hyper-Threading, it has 4MB of Level 3 cache and a TDP of 73W. As well as the unlocked multiplier, both chips still feature Intel's Turbo Boost technology, which automatically adjusts core frequency based on the CPU's workload.
In terms of pricing, the unlocked Core i5 655K will command a $40 price premium over the locked i5 650, while the Core i7 875K, at $349, is actually almost $240 cheaper than the locked Core i7 870. The new K-series models will officially launch at Computex next week, but there's a bunch of coverage floating around already. You can read some reviews at AnandTech, PC Perspective and The Tech Report.