In the comparison between the Intel® Core™ i7-2600 vs. the Intel Core i5-2500K, the main thing you should look at is what you are going to be doing with the processor. If you are going to be mainly gaming then the Intel Core i5-2500K is going to be the better processor for you. Right now very few games will take advantage of more than 3 threads, so the value of hyper-threading in minimal for gaming. Now if you are going to be doing video/audio or some other heavy multi-threaded work than the value of the Intel Core i7-2600 goes up a great deal.
In the battle of features Intel Core i7-2600 vs. Intel Core i5-2500K:
Intel Core i7-2600:
-Hyper-threading (giving total support for up to 8 threads)
-100MHz faster
-Support VT-d (directed I/O)
-Support for TXT (Trusted Execution Technology)
-Intel HD 2000 graphics
Intel Core i5-2500K:
-Unlocked multiplier (allows the processor to be overclocked)
-Intel HD 3000 graphics
http://ark.intel.com/Compare.aspx?ids=52213,52210,
Christian Wood
Intel Enthusiast Team