The best replacement for i5 2500k is i5 3570k.

The best alternatives to i5 2500k are rated as following:
★★★★★  i5 3570k
★★★★  i5 4670k
★★★★  i7 2600k
★★★  i7 3770k
★★  fx 8350
★★  i7 4770k
★★  fx 8320
★★  fx 6300
★  i7 920
★  i5 3470
★  i3 4340
★  i5 2500
★  fx 6350
  i7 950
  i5 2550k
  phenom x6
  i5 4670
  3570k
  i5 760
  i7 2700k
  i5 3330
  1100t

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Speaking about i5 2500k, one probably shouldn't forget about gtx 770.

Other search terms related to i5 2500k and their ratings are:
★★★★★ gtx 770
★★★★★ gtx 780
★★★★ gtx 780 ti
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Google Trends

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i5 2500k
i5 3570k
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