The Intel Core i7-4790K runs cooler than the Intel Core i7-4770K on stock thermal compound, with fans at stock voltage and frequencies. With a full load under Prime95, the Intel Core i7-4770K has a TDP of close to 185W, which can account for the heat difference. Ironically, the thermal advantage evens out the closer you get to that sweet 5 GHz overclock.
The higher the frequency, the better does the Intel Core i7-4770K actually holds up against the Intel Core i7-4790K. One would think the stepping of frequency to go hand in hand with the 4.5 degrees Celsius temperature barrier throughout, but Intel's Next Generation Processor Thermal Interface Material (NGPTIM) either has issues at higher overclocks or our specific CPU is just not built to get there as efficiently.