Would it be possible to reach 5ghz stable with any of these???
The ability to reach 5GHz is more dependant on your CPU specifically...not all CPUs are the same, and only a small percentage of each batch can get to 5GHz due to microscopic differences in individual CPUs from the same batch. The higher the targeted clock speed, the more unlikely you are to get there, sort of thing. 4.5 - 4.7GHz should be attainable.
The i5-2500K is a cool-running CPU so high-end air or closed-loop water will do you. Asus have an overclocking guide where they got an i5-2500K to exceed 5GHz with a Hyper-212; just bear in mind that the better the cooler, the lower the temps and the more longevity you'll get from a CPU.