Right now on Newegg the Intel® Core™ i7-2600K is $299.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115070
and the Intel Core i5-3570K is $229.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16819116504
The Intel Core i7-2600K does have hyper-threading but unless the way games are written changes soon it won't make a bit of difference. Also since the Intel Core i5-3570K has better IPC performance it does have to clock as high as the Intel Core i7-2600K to get the same results.
If you are going to do something that will take advantage of the hyper-threading by all means go with it. However if you are trying to build a gaming system forget about the Intel Core i7-2600K and go with the Intel Core i5-3570K.