Originally Posted by
lloewe
The equivalent would probably be the i5-6600k plus a Z170 chipset for easy overclocking.
However if you don't want to overclock you can also pick an i5-6500 with an H170.
Don't expect a huge performance gain though you're looking at maybe 10-15%.
Since the 2500Ks tend to overclock quite well overclocking your existing setup is most likely the best option if you're looking for some moderate improvements- especially if you can put the saved money to good use somewhere else (e.g. SSD).