Even though the 875K is a Core i7 processor both are socket 1156 and share the same heatspreader and pin schematic.
The Core i7-875K (45nm) is a 95W processor which runs at 2.93ghz and when Turbo Mode is enabled up to 3.6ghz. This is reached via a 133mhz BCLK and 22x multiplier. There is 4x32kb of Level 1 cache, 4x256kb of Level 2 cache and 8mb of shared L3 cache. Intel tolerance state that 1.4 volt is the maximum recommended, but once they get into the hands of extreme overclockers you can be assured this figure will be totally ignored.
The Core i5-655k (32nm) operates at 3.2ghz and up to 3.46ghz in Turbo mode using a 133mhz BCLK with a 24x multiplier. As we mentioned earlier, this also has an unlocked memory controller which is fully integrated offering official support for 1333mhz dual channel modules.
Interestingly, the 655k also features a graphics processing unit which is 45nm and contains 177 million transistors. This graphics processor is designed to operate with the H55/H57 chipsets and has a 900mhz core with Third Generation Shader Architecture and 12 execution units. It also has support for AVC/VC-1 decode which will please media users and offers Noise Reduction with HDMI/Displayport line outs. Additionally Intel offer Dolby TrueHD and DTS HD Master Audio.