The significant difference between the 'K' and non 'K' processors is quite simple, the K processors can be over clocked, while the non K processors cannot. The K processors have an "unlocked" multiplier (aka Turbo multiplier) which can be changed in a mother boards BIOS (that supports that feature), while the non K processors cannot have their multiplier changed. When I say changed, I mean cannot be changed or increased above a certain number.
An Ivy Bridge or Sandy Bridge processors speed or operating frequency is determined by the multiplier, and what is called the BCLK, or Base Clock. BCLK X multiplier = processors speed/frequency. BCLK = 100MHz.
So 100 MHz X 34 (the multiplier) results in a speed of 3,400MHz, or 3.4GHz. Turbo boost sets the multiplier to 39. Non K processors cannot be set to a multiplier above 39. The multiplier of the i7-3770K can be set to I believe 60 - 62. In reality, that processors will usually only operate with the multiplier set to 45 or 46, or a speed of 4.6Ghz. Sandy Bridge K processors can operate with a multiplier of 50, at 5.0GHz. That is, given expensive, after market CPU coolers, expensive mother boards and power supplies, etc, and experience.
Intel does not really market this feature, or show it in the specifications, but PC enthusiasts are aware of it and use those processors. They gladly trade the other features and higher price for the ability to run their processors faster than the norm. It's like a sports car, fast and quick, but a tradeoff in other features.