Like i said , 3rd gen i5 3570k is much slower than 4th gen i5 4670k . i5 4670k @ 4.2GHz is on par with i5 3570k @ 5.0GHz in Dolphin Benchmark and you won't be able to overclock i5 3570k pass the limit : 4.5GHz without using insanely high vcore (damage CPU) . It would be wasteful if you paired an unlocked multiplier CPU with a locked mobo (H61/H77/B75)
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