I can't seem to get a straight answer to this question, so I thought I'd ask on the intel forums to put it to bed once and for all.
On the H77 chipset specification, it says "Supports the 3rd generation Intel® Core™ processors with Turbo Boost Technology 2.0 Intel® Pentium® processor, and Intel® Celeron® processor. Intel H77 Express Chipset also enables overclocking features of unlocked 3rd generation Intel® Core™ processors".
2. Suppose I own an i5-2500K and a H77 motherboard. I cannot overclock this CPU to 4.5GHz as described above, but can still increase its clock speed to its max turbo frequency of 3.7GHz. Correct, yes or no? http://ark.intel.com/products/52210
In theory the answer for your two questions is yes but Intel's position is that the operation of any Intel-manufactured product outside the published specifications for each part, such as overclocking, can result in data corruption and unreliable system behavior. It will shorten the life of your product, void the warranty of your processor, your motherboard, and possibly other devices installed in the computer. There is no support from Intel for overclocking.