Clean install is HIGHLY recommended.
The problem is Drivers. So cloning is OUT. There are a few programs that will migrate the OS from one drive to another. Basically what they do is strip out the drivers (ie in device manager) and when you first boot into windows on the new system it will be forced to re-load the windows default drivers, BUT YOU will still need to update many of the MB specific drivers for optium performance.
OK Ignore below as you explained why - LOL Did not delet as others may have the same Idea of Upgrading a i5-2500K -> i5 IB CPU.
You might want to save some money by going with the Newer Z77 MB but retain your 2500K.
.. CPUs VERY little difference between them maybe 10% performance gain, which is Hardly...